Electrolytes for Lithium Batteries with Carbon and/or Silicon Anodes

ABSTRACT

Electrolytes for lithium ion batteries with carbon-based, silicon-based, or carbon- and silicon-based anodes include a lithium salt; a nonaqueous solvent comprising at least one of the following components: (i) an ester, (ii) a sulfur-containing solvent, (iii) a phosphorus-containing solvent, (iv) an ether, (v) a nitrile, or any combination thereof, wherein the lithium salt is soluble in the solvent; a diluent comprising a fluoroalkyl ether, a fluorinated orthoformate, a fluorinated carbonate, a fluorinated borate, or a combination thereof, wherein the lithium salt has a solubility in the diluent at least 10 times less than a solubility of the lithium salt in the solvent; and an additive having a different composition than the lithium salt, a different composition than the solvent, and a different composition than the diluent.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the earlier filing dates of U.S.Provisional Application No. 63/080,486, filed Sep. 18, 2020, U.S.Provisional Application No. 62/970,651, filed Feb. 5, 2020, and U.S.Provisional Application No. 62/959,051, filed Jan. 9, 2020, each ofwhich is incorporated by reference herein in its entirety.

ACKNOWLEDGMENT OF GOVERNMENT SUPPORT

This invention was made with Government support under Contract No.DE-AC05-76RL01830 and Award Number DE-EE0008444, both awarded by theU.S. Department of Energy. The Government has certain rights in theinvention.

FIELD

This invention is directed to electrolytes for stable cycling oflithium-ion batteries including carbon-based, silicon-based, orcarbon/silicon composite-based anodes, and cathodes with intercalationcompounds or conversion compounds.

BACKGROUND

Lithium (Li)-ion batteries (LIBs) are indispensable power sources forportable electronic devices, electric vehicles, stationary or gridapplications, and the like. However, further efforts on extending thecycle life, rate capability, energy density and working temperaturerange and improving the safety of LIBs are required to addresssignificant challenges for their large-scale applications. Two of themost feasible and effective approaches to meet the energy density demandare increasing the specific capacity of the intercalation cathodes suchas LiCo₂ (LCO) or LiNi_(x)Mn_(y)Co_(1−x−y)O₂ (NMC) and elevating thecharge cut-off voltage of the LIBs. Increasing Ni content in NMCcathodes is expected to significantly boost the specific capacity of theNMC cathodes. In addition, elevating the charge cut-off voltage canincrease both the specific capacity and the average voltage of the NMCcathodes. By combining these two approaches, the specific energy of thehigh-Ni NMC based LIBs can be significantly improved. However, theenergy increase by these two approaches is usually achieved at the costof shortened battery lifespan due to the intrinsic structuralinstability of the cathode material at high charge cut-off voltages(de-lithiation state) (Mao et al., Advanced Functional Materials 2019,29(18): 1900247; Goonetilleke et al., Chemistry of Materials 2018,31(2): 376-386), the continuous electrolyte decomposition at the cathodesurface caused by its insufficient thermodynamic stability towards Ni⁴⁺at high operation voltages (Zhu et al., Journal of Power Sources 2014,246: 184-191), and the detrimental interactions between cathodematerials and anode materials caused by state-of-the-art LiPF₆-basedelectrolytes (Jia et al., Chemistry of Materials 2019, 31(11):4025-4033). The practical application of Ni-rich NMC cathode materialsis greatly hindered by the poor cathode-electrolyte interface (CEI)layer formed on such cathode surface in the state-of-the-artelectrolytes comprised of lithium hexafluorophosphate (LiPF₆) incarbonate solvents, especially at voltages higher than 4.3 V vs. Li/Li⁺,causing continuous electrolyte oxidative decomposition and other relatedside reactions such as transition metal dissolution from the cathodesurface, thus leading to poor cycling stability, especially at elevatedtemperatures and high operating voltages. At the same time, thepractical application of electrolytes in LIBs must also take intoaccount the electrolyte compatibility with the graphite (Gr)- and/orsilicon (Si)-based anodes through the formation of high quality solidelectrolyte interface (SEI) films. A need exists for electrolytes thatare stable towards the anode and cathode, are operable over a widevoltage window and a wide temperature range, and enable batteries withdesirable specific energy, capacity retention, and/or cycling lifetimes.

SUMMARY

Electrolytes for use in LIBs are disclosed, as well as LIBs includingthe electrolytes. Embodiments of the disclosed electrolytes include alithium salt; a nonaqueous solvent comprising at least one of thefollowing components (i) an ester, (ii) a sulfur-containing solvent,(iii) a phosphorus-containing solvent, (iv) an ether, (v) a nitrile, or(vi) any combination thereof, wherein the lithium salt is soluble in thesolvent; a diluent comprising at least one of the following components:a fluoroalkyl ether, a fluorinated orthoformate, a fluorinatedcarbonate, a fluorinated borate, or a combination thereof, wherein thelithium salt has a solubility in the diluent at least 10 times less thana solubility of the lithium salt in the solvent; and an additive havinga different composition than the lithium salt, a different compositionthan the solvent, and a different composition than the diluent. Theelectrolyte has a lithium salt-solvent-additive-diluent molar ratio of1:x:y:z where 0.5≤x≤5, 0≤y≤1, and 0.5≤z≤5.

In any of the foregoing or following embodiments, the lithium salt maycomprise lithium bis(fluorosulfonyl)imide (LiFSI), lithiumbis(trifluoromethanesulfonyl)imide (LiTFSI), lithium(fluorosulfonyl)(trifluoromethylsulfonyl)imide (LiFTFSI), lithiumbis(pentafluoroethanesulfonyl)imide (LiBETI), lithiumtrifluoromethanesulfonate (LiTf), lithium bis(oxalato)borate (LiBOB),LPF₆, LAsF₆, LiBF₄, LiCF₃SO₃, LiClO₄, lithium difluoro(oxalato)borate(LiDFOB), LiI, LiBr, LiCl, LiSCN, LiNO₃, LiNO₂, Li₂SO₄, or anycombination thereof. In any of the foregoing or following embodiments,the nonaqueous solvent may comprise dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), diethyl carbonate (DEC), ethylene carbonate(EC), propylene carbonate (PC), difluoroethylene carbonate (DFEC),trifluoroethylene carbonate (TFEC), trifluoropropylene carbonate (TFPC),methyl 2,2,2-trifluoroethyl carbonate (MFEC), ethyl acetate, ethylpropionate, methyl butyrate, ethyl trifluoroacetate,2,2,2-trifluoroethyl acetate, 2,2,2-trifluoroethyl trifluoroacetate,dimethyl sulfone (DMS), ethyl methyl sulfone (EMS), ethyl vinyl sulfone(EVS), tetramethylene sulfone (TMS), dimethyl sulfoxide, ethyl methylsulfoxide, trimethyl phosphate (TMPa), triethyl phosphate (TEPa),tributyl phosphate, triphenyl phosphate, tris(2,2,2-trifluoroethyl)phosphate, bis(2,2,2-trifluoroethyl) methyl phosphate, trimethylphosphite, triphenyl phosphite, tris(2,2,2-trifluoroethyl) phosphite,dimethyl methylphosphonate, diethyl ethylphosphonate, diethylphenylphosphonate, bis(2,2,2-trifluoroethyl) methylphosphonate,hexamethylphosphoramide, hexamethoxyphosphazene(cyclo-tris(dimethoxyphosphonitrile), hexamethoxycyclotriphosphazene),hexafluorophosphazene (hexafluorocyclotriphosphazene),1,2-dimethoxyethane (DME), diethylene glycol dimethyl ether (DEGDME, ordiglyme), triethylene glycol dimethyl ether (triglyme), tetraethyleneglycol dimethyl ether (tetraglyme), 1,3-dioxolane (DOL), allyl ether,acetonitrile, propionitrile, or any combination thereof. In any of theforegoing or following embodiments, the additive may comprise EC, FEC,VC, 4-vinyl-1,3-dioxolan-2-one (VEC), 4-methylene-1,3-dioxolan-2-one(4-methylene ethylene carbonate (MEC)),4,5-dimethylene-1,3-dioxolan-2-one, 4-vinyl-1,3-dioxolan-2-one,prop-1-ene-1,3-sultone (PES), 1,3,2-dioxathiolane-2-oxide,1,3,2-dioxathiolane-2,2-dioxide, 1,3,2-dioxathiane-2,2-dioxide (DTD),lithium 2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI), lithiumdifluoro(oxalate)borate (LiDFOB, if not used as a lithium salt), lithiumhexafluorophosphate, 3-methyl-,4,2-dixoazol-5-one (MDO),tris(2,2,2-trifluoroethyl) phosphite (TTFEPi), 2-oxo-1,3,2-dioxathiane,butanedinitrile, pentanedinitrile, hexanedinitrile,tris(pentafluorophenyl) phosphine, 1-methylsulfonylethene,1-ethenylsulfonylethane, or any combination thereof. In any of theforegoing or following embodiments, the diluent may comprise1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE),bis(2,2,2-trifluoroethyl) ether (BTFE), 1H,1H,5H-octafluoropentyl1,1,2,2-tetrafluoroethyl ether (OTE), 1,2,2,2-tetrafluoroethyltrifluoromethyl ether, heptafluoroisopropyl methyl ether,tris(2,2,2-trifluoroethyl) orthoformate (TFEO),bis(2,2,2-trifluoroethyl) carbonate, tris(2,2,2-trifluoroethyl) borate,or any combination thereof.

In some embodiments, the nonaqueous solvent comprises DMC, DME, TMS,TMPa, TEPa, or any combination thereof. In certain embodiments, (i) thesalt comprises LiFSI; or (ii) the diluent comprises TTE, BTFE, OTE, orany combination thereof; or (iii) the additive comprises EC, FEC, VC, orany combination thereof; or (iv) any combination of (i), (ii), and(iii).

Embodiments of a battery system include an electrolyte as disclosedherein, an anode, and a cathode. The anode may be a carbon-based anode,a Si-based anode, or a anode based on composite of carbon and Si. Insome examples, the anode is a Gr-based anode, a Si-based anode, a Si/Grcomposite anode comprising 10 wt % to 95 wt % Gr and 5 wt % to 90 wt %Si, or a silicon/carbon composite anode comprising carbon-coated Si witha carbon (C) content of 5 wt % to 55 wt %. In certain examples, thecathode comprises LiNi_(x)Mn_(y)Co_(z)O₂ where x≥0.6 orLiNi_(x)Mg_(y)T_(1−x−y)O₂ where 0.9≤x<1.

The foregoing and other objects, features, and advantages of theinvention will become more apparent from the following detaileddescription, which proceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

FIGS. 1A and 1B are schematic diagrams of a conventionalsuperconcentrated electrolyte or high concentration electrolyte (HCE)(1A) and a localized superconcentrated electrolyte (LSE) or localizedhigh-concentration electrolyte (LHCE) (1B).

FIGS. 2A and 2B are schematic diagrams of an exemplary rechargeablebattery (1A) and a side elevation view of a simplified pouch cell (1B).

FIG. 3 is a graph showing the capacity retention of Si/Gr∥NMC532 cellswith a baseline electrolyte and several DMC-based localizedhigh-concentration electrolytes (LHCEs, La and Lb) disclosed herein, andcycled between an operating voltage window of 3 V to 4.1 V for 300cycles.

FIG. 4 is a graph showing the Coulombic efficiency (CE) of theSi/Gr∥NMC532 cells of FIG. 3 over the 300 cycles.

FIG. 5 is a graph showing the capacity retention of Si/Gr∥NMC532 cellswith a baseline electrolyte and several additional DMC-based LHCEs(Lc1-Lc7) disclosed herein, and cycled between an operating voltagewindow of 3 V to 4.1 V for 300 cycles.

FIG. 6 is a graph showing the CE of the Si/Gr∥NMC532 cells of FIG. 5over the 300 cycles.

FIG. 7 shows the first cycle cyclic voltammetry curves of Li∥Gr cellswith a baseline electrolyte and three DMC-based LHCEs (AE001-AE003) asdisclosed herein between 0.02-2.0 V at a scan rate of 0.1 mV-s⁻¹.

FIGS. 8A and 8B show the temperature dependence of ionic conductivities(8A) and viscosities (8B) of the electrolytes of FIG. 7.

FIG. 9 shows linear sweep voltammetry (LSV) curves on SP-PVDF/AIelectrode in three-electrode cells with Li as counter and referenceelectrodes and SP-PVDF/AI as working electrode at a scan rate of 0.1mV-s⁻¹.

FIG. 10 shows the voltage profiles of the first formation cycle at C/20rate at 25° C. between 2.5 and 4.4 V for Gr∥NMC811 coin cells with abaseline electrolyte and three DMC-based LHCEs as disclosed herein.

FIGS. 11A and 11B show long-term cycling stability of the cells of FIG.10 at C/3 rate at 25° C. (11A) and 60° C. (11B) after three formationcycles at 25° C.

FIGS. 12A-12E show the long-term cycling performance of the Gr∥NMC811coin cells of FIG. 10 at C/3 rate in the voltage range of 2.5-4.4 V at25° C.; FIG. 12A shows the CE with the insets showing the CE values ofthe three formation cycles and the CEs between 350-450 cycles;

FIGS. 12B-12E show the voltage profiles at selected cycles with thebaseline electrolyte (12B), AE001 electrolyte (12C), AE002 electrolyte(12D), and AE003 electrolyte (12E).

FIGS. 13A-13F show the long-term cycling performance of the Gr∥NMC811coin cells of FIG. 10 at C/3 rate in the voltage range of 2.5-4.4 V at60° C., with three formation cycles at 25° C.;

FIG. 13A shows the CEs of the three formation cycles; FIG. 13B shows thecycling efficiency over 100 cycles; FIGS. 13C-13F show the voltageprofiles at selected cycles during cycling with the baseline electrolyte(13C), AE001 electrolyte (13D), AE002 electrolyte (13E), and AE003electrolyte (13F).

FIG. 14 shows Nyquist plots of the Gr∥NMC811 coin cells of FIG. 10 after3 formation cycles at 25° C. (lower panel) and after 100 cycles at 60°C. (upper panel).

FIGS. 15A-15F show the long-term cycling performance of the Gr∥NMC811coin cells of FIG. 10 at C/3 rate in the voltage range of 2.5-4.4 V at60° C., with three formation cycles at 60° C.; FIG. 15A shows the CEover 100 cycles; FIG. 15B shows the discharge capacity over 100 cycles;FIGS. 15C-15F show the voltage profiles at selected cycles duringcycling with the baseline electrolyte (15C), AE001 electrolyte (15D),AE002 electrolyte (15E), and AE003 electrolyte (15F).

FIGS. 16A and 16B show rate capabilities of the Gr∥NMC811 coin cells ofFIG. 10 under varying discharge rates (xC, FIG. 16A) with the samecharge rate at C/5, and varying charge rates (xC, FIG. 16B) with thesame discharge rate at C/5.

FIG. 17 is a Walden plot of the baseline electrolyte and the threeDMC-based LHCEs according to conductivity and viscosity withtemperature.

FIG. 18 shows the low-temperature discharge performance of the Gr∥NMC811coin cells of FIG. 10 at C/5 discharge rate. The operating temperaturefor all charging process was 25° C. while the discharging was conductedat 25° C., 0° C., −10° C., −20° C., −30° C. and −40° C., and then backto 25° C. The inserted diagram shows the discharge capacities at 25° C.before and after the low-temperature discharging. 1C corresponds to 2.8mA cm⁻².

FIGS. 19A-19D show voltage profiles of the Gr∥NMC811 coin cells of FIG.10 during low-temperature discharging tests in the temperature range of25° C. to −40° C. at C/5 charge/discharge rate between 2.5-4.4 V withthe baseline electrolyte (19A), AE001 electrolyte (19B), AE002electrolyte (19C), and AE003 electrolyte (19D). Three formation cycles(first at C/20 and the other two at C/10) were conducted at 25° C.before the low-temperature testing. The operating temperature forcharging is 25° C. and the temperatures for discharging are 25° C., 0°C., −10° C., −20° C., −30° C. and −40° C., respectively, then back to25° C.

FIG. 20 shows differential scanning calorimetry (DSC) curves of theE-baseline, and the AE001, AE002, and AE003 LSEs.

FIG. 21 shows x-ray diffraction (XRD) patterns of the pristine Gr anodeand the cycled Gr anodes in E-baseline and the LSEs after 100 cycles at60° C.; the inset image is the expanded view of (002) reflection.

FIGS. 22A-22E are scanning electron microscopy images of the pristine Granode (22A) and the cycled Gr anodes in E-baseline (22B), AE001electrolyte (22C), AE002 electrolyte (22D), and AE003 electrolyte (22E)after 100 cycles at 60° C.

FIGS. 23A-23E are high-resolution transmission electron microscopy(HRTEM) images of the pristine Gr anode (23A) and the cycled Gr anodesin E-baseline (23B), AE001 electrolyte (23C), AE002 electrolyte (23D),and AE003 electrolyte (23E) after 100 cycles at 60° C.

FIG. 24 shows quantified atomic composition ratios of the elements inthe SEI layer from the baseline, AE001, AE002, and AE003 electrolytes byx-ray photon spectroscopy.

FIG. 25 shows XPS spectra of C 1s, O 1s, and F 1s on pristine Gr anodeand Gr anodes cycled in E-baseline and AE003 electrolytes.

FIG. 26 shows XPS spectra of SEI components on cycled Gr anodes after100 cycles at 60° C. in the E-baseline, AE001, AE002, and AE003electrolytes.

FIGS. 27A-27J are SEM images of pristine NMC811 cathode (27A, 27B), andNMC811 cathodes cycled in Gr∥NMC811 cells with E-baseline (27C, 27D),AE001 (27E, 27F), AE002 (27G, 27H), and AE003 (271, 27J) electrolytesfor 100 cycles at 60° C.

FIGS. 28A-28J are cross-sectional FIB/SEM images of NMC811 particles(28A-28E) and HRTEM images of the CEI layer morphologies on NMC811cathodes (28F-28J) cycled in the E-baseline, AE001, AE002, and AE003electrolytes.

FIGS. 29A-29B are XRD patterns of (003) (29A) and (108)/(110) (29B)peaks of NMC811 cathodes cycled in the E-baseline, AE001, AE002, andAE003 electrolytes.

FIGS. 30A-30D show the XPS atomic ratios of elements (30A) and XPSspectra of C 1s (30B), O 1s (30C), and F 1s (30D) of the CEI from apristine NMC811 cathode and NMC811 cathodes after 100 cycles at 60° C.in the E-baseline and AE003 electrolytes.

FIG. 31 shows XPS spectra of CEI components on cycled NMC811 cathodesafter 100 cycles at 60° C. in the electrolytes of E-baseline (for P 2p),AE001 (for C 1s, O 1s, F 1s, N 1s and S 2p), AE002 (for C 1s, O 1s, F1s, N 1s and S 2p), and AE003 (for N 1s and S 2p).

FIGS. 32A and 32B show first cycle CV curves of Li∥Gr cells withE-baseline, AE001, AE002, AE003, AE004, and AE005 electrolytes between0.02-2.0 V at a scan rate of 0.1 mV·s⁻¹ (32A) and LSV curves onSP-PVDF/AI electrode in three-electrode cells with Li as counter andreference electrodes at a scan rate of 0.1 mV-s⁻¹ (32B).

FIGS. 33A-33F show battery performances of the E-baseline, AE001, AE002,AE003, AE004, and AE005 electrolytes in Gr∥NMC811 coin cells between 2.5and 4.4 V: voltage profiles of the first formation cycle at C/20 rateand 25° C. (33A); long-term cycling stability at C/3 rate at 25° C.(33B) and 60° C. (33C) after three formation cycles at 25° C.; ratecapabilities under varying discharge rates (xC, 33D) with the samecharge rate at C/5, and varying charge rates (xC, 33E) with the samedischarge rate at C/5; low-temperature discharge performance at C/5discharge rate (33F); the operating temperature for all charging processwas 25° C. while the discharging was conducted at 25° C., 0° C., −10°C., −20° C., −30° C. and −40° C., and then back to 25° C. 1C correspondsto 2.8 mA cm⁻².

FIGS. 34A-34G show the long-term cycling performance of Gr∥NMC811 coincells with E-baseline AE001, AE002, AE003, AE004, and AE005 electrolytesat C/3 rate in the voltage range of 2.5-4.4 V at 25° C.: the Coulombicefficiency (CE) during the long-term cycling (34A); the voltage profilesat selected cycles during cycling (34B-34G).

FIGS. 35A-35G show the long-term cycling performance of Gr∥NMC811 coincells with E-baseline, AE001, AE002, AE003, AE004, and AE005electrolytes at C/3 rate in the voltage range of 2.5-4.4 V at 60° C.,with three formation cycles performed at 25° C.: the Coulombicefficiency (CE) during the long-term cycling (35A); the voltage profilesat selected cycles during cycling (35B-35G).

FIGS. 36A-36B show the temperature dependence of ionic conductivitiesfrom −40 to 60° C. (36A) and viscosity from −7 to 50° C. (36B) of theE-baseline, AE001, AE002, AE003, AE004, and AE005 electrolytes.

FIGS. 37A-37F show voltage profiles of Gr∥NMC811 coin cells using theE-baseline (37A), AE001 (37B), AE002 (37C), AE003 (37D), AE004 (37E),and AE005 (37F) electrolytes during low-temperature discharging test inthe temperature range of 25° C. to −40° C. and then back to 25° C. (theblack dotted line) at C/5 charge/discharge rate between 2.5-4.4 V.

FIG. 38 shows the long-term cycling performance of Gr∥NMC811 coin cellswith various LHCEs without vinylene carbonate (VC) and comparison withtwo baseline electrolytes without (E257) and with (E268) 2 wt % VC at25° C.; the discharge capacity shows the average value with standarddeviation.

FIGS. 39A-39B show temperature dependence of viscosities (39A) and ionicconductivities (39B) of a baseline electrolyte with 2 wt % VC andseveral DME-based LHCEs.

FIGS. 40A-40B show charge/discharge voltage-specific capacity profilesat the first formation cycle at C/20 rate (40A) and CE comparison in theformation cycles (40B) of Gr∥NMC811 cells with the electrolytes of FIGS.39A-39B.

FIGS. 41A-41B show the specific discharge capacity of the Gr∥NMC811cells of FIGS. 40A-40B (1×charge/discharge cycle at C/20 and2×charge/discharge cycles at C/10 as formation cycle, followed by500×charge at C/3 discharge at 1C cycles) (41A) and the CE of the cells(41B).

FIG. 42 shows the discharge rate capability of Gr∥NMC811 cells of FIGS.40A-40B at 25.0±0.1° C. over a voltage range of 2.5-4.4 V.

FIG. 43 shows the average specific discharge capacity of Gr∥NMT coincells comprising a baseline electrolyte or an LHCE comprisingLiFSI:DME:TTE:FEC=1.0:1.1:3.0:0.2 by mol over 500 cycles at 25° C.

FIG. 44 shows long-term cycling performance of Gr∥NMT coin cellscomprising a baseline electrolyte or an LHCE comprisingLiFSI:DMC:TTE:FEC=1.0:2.0:3.0:0.2 by mol at 25° C.

FIGS. 45A-45B show temperature dependence of viscosities (45A) and ionicconductivities (45B) of a baseline electrolyte and several TMPa-basedLHCEs.

FIG. 46 shows the anodic stability voltages of the electrolytes of FIGS.45A-45B determined by linear sweep voltammetry at the scan rate of 0.1mV s⁻¹.

FIGS. 47A-47B show the C-rate performance (47A) and average specificdischarge capacity as a function of cycle number (47B) of Gr∥NMC811cells using a baseline and several TMPa-based LHCEs.

FIG. 48 shows the average specific discharge capacity of Gr∥NMC811 cellscomprising a baseline electrolyte and TMS-based LHCEs plotted as afunction of cycle number.

FIGS. 49A-49D show battery performances of a baseline electrolyte andtwo DMC-based LHCEs in Si/C∥NMC811 coin cells between 2.8 and 4.4 V:voltage profiles of the first formation cycle at C/20 rate and the firstcycle at C/3 at 25° C. (49A); long-term cycling stability at C/3 rate at25° C. (49B) and 45° C. (49C) after three formation cycles at 25° C.;rate capabilities under varying discharge rates (xC) with the samecharge rate at C/10 (1C corresponds to 5.0 mA cm⁻²) (49D).

FIG. 50 shows long-term cycling specific capacity of Si∥NMC622 coincells with a baseline electrolyte and four DMC-based LHCEs at 25° C. at0.7C charge and C/2 discharge after a formation cycle of C/10 in the1^(st) cycle and C/5 for the 2^(nd) cycle. Capacity check at C/5 atevery 50 cycles. Si with 30% capacity pre-lithiation.

FIG. 51 shows long-term cycling CE of the coin cells of FIG. 50.

FIGS. 52A-52B show the voltage profiles of Si∥NMC622 coin cells using aSi-baseline electrolyte (52A) and a DMC-based LHCE (52B) at 25° C. at0.7C charge and C/2 discharge after formation cycle of C/10 in the1^(st) cycle and C/5 for the 2^(nd) cycle. Capacity check at C/5 atevery 50 cycles. Si with 30% capacity pre-lithiation.

FIG. 53 shows long-term cycling specific capacity of Si∥NMC622 coincells with a baseline electrolyte and four DMC-based LHCEs at 45° C.after a formation cycle of C/10 in the 1^(st) cycle and C/5 for the2^(nd) cycle at 25° C. Capacity check at C/5 at every 50 cycles. Siwithout pre-lithiation.

FIG. 54 shows long-term cycling CE of the coin cells of FIG. 53.

FIGS. 55A-55B show battery performances of a baseline electrolyte andseveral LHCEs in Si/C∥NMC811 coin cells between 2.8 and 4.4 V at 25° C.:voltage profiles of the first formation cycle at C/20 rate (55A);cycling stability at C3 rate, 1C corresponds to 5.0 mA cm⁻² (55B).

FIGS. 56A-56C show the radial distribution function between Li and Oatoms of different molecules in DME-based LHCEs: E-DME (56A), E-DME-E(56B), and E-DME-F (56C).

FIGS. 57A-57B show self-diffusion coefficients of different species inthe baseline electrolyte (57A) and the electrolytes of FIGS. 56A-56C(57B).

FIG. 58 shows atomic concentrations of elements in the SEIs formed on Granodes in the baseline, E-DME, E-DME-E, and E-DME-F electrolytes.

FIG. 59 shows XPS C 1s, O 1s, F 1s, N 1s, and S 2p spectra of SEs formedon Gr anodes in the baseline, E-DME, E-DME-E, and E-DME-F electrolytesafter 3 formation cycles.

FIG. 60 shows XPS C 1s, O 1s, F 1s, N 1s, and S 2p spectra of SEs formedon Gr anodes in the baseline, E-DME, E-DME-E, and E-DME-F electrolytesafter 500 charge/discharge cycles.

FIGS. 61A-61H are TEM images showing morphologies of SEIs formed on Grparticles after 3 formation cycles (61A-61D, respectively) and 500charge/discharge cycles (61E-61H, respectively) in the baseline, E-DME,E-DME-E, and E-DME-F electrolytes.

FIGS. 62A-62B show XRD patterns of Gr particles retrieved from Grelectrodes after 500 charge/discharge cycles in the baseline, E-DME,E-DME-E, and E-DME-F electrolytes.

FIG. 63 shows anodic stability voltages of the baseline, E-DME, E-DME-E,and E-DME-F electrolytes determined by LSV.

FIGS. 64A-64H are TEM images showing morphologies of NMC811 particlesafter 3 formation cycles (64A-64D, respectively) and 500charge/discharge cycles (64E-64H, respectively) in the baseline, E-DME,E-DME-E, and E-DME-F electrolytes.

DETAILED DESCRIPTION

This disclosure concerns embodiments of localized superconcentratedelectrolytes (LSEs), or localized high-concentration electrolytes(LHCEs), for use in systems, such as LIB systems. Systems including theLHCEs are also disclosed. Some embodiments of the disclosed LHCEs arestable in electrochemical cells with silicon-based,carbon/silicon-based, or carbon-based (e.g., graphite- and/or hardcarbon-based) anodes and various cathode materials. The LHCEs comprise alithium salt, a nonaqueous solvent in which the lithium salt is soluble,a diluent in which the lithium salt is insoluble or poorly soluble, andan additive having a different composition than the lithium salt, adifferent composition than the solvent, and a different composition thanthe diluent. The LHCE has a lithium salt-solvent-additive-diluent molarratio of 1:x:y:z where 0.5≤x≤5, 0≤y≤1, and 0.5≤z≤5.

1. Definitions and Abbreviations

The following explanations of terms and abbreviations are provided tobetter describe the present disclosure and to guide those of ordinaryskill in the art in the practice of the present disclosure. As usedherein, “comprising” means “including” and the singular forms “a” or“an” or “the” include plural references unless the context clearlydictates otherwise. The term “or” refers to a single element of statedalternative elements or a combination of two or more elements, unlessthe context clearly indicates otherwise.

Unless explained otherwise, all technical and scientific terms usedherein have the same meaning as commonly understood to one of ordinaryskill in the art to which this disclosure belongs. Although methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the present disclosure, suitable methods andmaterials are described below. The materials, methods, and examples areillustrative only and not intended to be limiting. Other features of thedisclosure are apparent from the following detailed description and theclaims.

Unless otherwise indicated, all numbers expressing quantities ofcomponents, molecular weights, molarities, voltages, capacities, and soforth, as used in the specification or claims are to be understood asbeing modified by the term “about.” Accordingly, unless otherwiseimplicitly or explicitly indicated, or unless the context is properlyunderstood by a person of ordinary skill in the art to have a moredefinitive construction, the numerical parameters set forth areapproximations that may depend on the desired properties sought and/orlimits of detection under standard test conditions/methods as known tothose of ordinary skill in the art. When directly and explicitlydistinguishing embodiments from discussed prior art, the embodimentnumbers are not approximates unless the word “about” is recited.

Although there are alternatives for various components, parameters,operating conditions, etc. set forth herein, that does not mean thatthose alternatives are necessarily equivalent and/or perform equallywell. Nor does it mean that the alternatives are listed in a preferredorder unless stated otherwise.

Definitions of common terms in chemistry may be found in Richard J.Lewis, Sr. (ed.), Hawley's Condensed Chemical Dictionary, published byJohn Wiley & Sons, Inc., 2016 (ISBN 978-1-118-13515-0).

In order to facilitate review of the various embodiments of thedisclosure, the following explanations of specific terms are provided:

Active salt: As used herein, the term “active salt” refers to a saltthat constitutes at least 5% of the redox active materials participatingin redox reactions during battery cycling after initial charging.

Additive: As used herein, the term “additive” refers to a component ofan electrolyte that is present in an amount of greater than zero andless than or equal to 10 wt % or less than or equal to 20 mol %.

Anode: An electrode through which electric charge flows into a polarizedelectrical device. From an electrochemical point of view,negatively-charged anions move toward the anode and/orpositively-charged cations move away from it to balance the electronsleaving via external circuitry. In a discharging battery or galvaniccell, the anode is the negative terminal where electrons flow out. Ifthe anode is composed of a metal, electrons that it gives up to theexternal circuit are accompanied by metal cations moving away from theelectrode and into the electrolyte. When the battery is recharged, theanode becomes the positive terminal where electrons flow in and metalcations are reduced. Unless otherwise specified, the term “anode” asused herein, refers to the negative electrode or terminal whereelectrons flow out during discharge.

BTFE: bis(2,2,2-trifluoroethyl)ether

Capacity: The capacity of a battery is the amount of electrical charge abattery can deliver. The capacity is typically expressed in units ofmAh, or Ah, and indicates the maximum constant current a battery canproduce over a period of one hour. For example, a battery with acapacity of 100 mAh can deliver a current of 100 mA for one hour or acurrent of 5 mA for 20 hours. The term specific capacity refers tocapacity per unit of mass. In this application, the mass specificallyrefers to the mass of the active material in the electrodes. Specificcapacity may be expressed in units of mAh/g. The term specific arealcapacity refers to capacity per unit of area of the electrode or activematerial. Specific areal capacity may be expressed in units of mAh/cm⁻².

Carbon- and silicon-based anode/negative electrode: A majority of thetotal anode mass is carbon (e.g., hard carbon, graphite) and silicon,such as at least 70 wt %, at least 80 wt %, or at least 90 wt % carbonand silicon.

Carbon/silicon composite: As used herein, the term carbon/siliconcomposite refers to a material including both carbon (such as graphiteand/or hard carbon) and silicon. A composite material is made from twoor more constituent materials that, when combined, produce a materialwith characteristics different than those of the individual components.Carbon/silicon composites may be prepared, for example, by pyrolysis ofpitch embedded with graphite and silicon powders (see, e.g., Wen et al.,Electrochem Comm 2003, 5(2):165-168).

Cathode: An electrode through which electric charge flows out of apolarized electrical device. From an electrochemical point of view,positively charged cations invariably move toward the cathode and/ornegatively charged anions move away from it to balance the electronsarriving from external circuitry. In a discharging battery or galvaniccell, the cathode is the positive terminal, toward the direction ofconventional current. This outward charge is carried internally bypositive ions moving from the electrolyte to the positive cathode, wherethey may be reduced. When the battery is recharged, the cathode becomesthe negative terminal where electrons flow out and metal atoms (orcations) are oxidized. Unless otherwise specified, the term “cathode” asused herein, refers to the positive electrode during discharge.

Cathode electrolyte interphase (CEI) layer: A passivation layercomprising electrolyte decomposition products formed on the cathode oflithium-ion batteries during the first few cycles.

Cell: As used herein, a cell refers to an electrochemical device usedfor generating a voltage or current from a chemical reaction, or thereverse in which a chemical reaction is induced by a current. A batteryincludes one or more cells. The terms “cell” and “battery” are usedinterchangeably when referring to a battery containing only one cell.

Consists essentially of: By “consists essentially of” is meant that theelectrolyte does not include other components that materially affect theproperties of the electrolyte alone or in a system including theelectrolyte. Electrolyte properties include, but are not limited to,Coulombic efficiency, cycling stability, voltage window, conductivity,viscosity, volatility, and flammability. For example, the electrolytedoes not include any electrochemically active component (i.e., acomponent (an element, an ion, or a compound) that is capable of formingredox pairs having different oxidation and reduction states, e.g., ionicspecies with differing oxidation states or a metal cation and itscorresponding neutral metal atom) other than the lithium salt in anamount sufficient to affect performance of the electrolyte, and does notinclude additional solvents, diluents, or additives, besides thoselisted, in a significant amount (e.g., >1 wt %).

Coulombic efficiency (CE): The efficiency with which charges aretransferred in a system facilitating an electrochemical reaction. CE maybe defined as the amount of charge exiting the battery during thedischarge cycle divided by the amount of charge entering the batteryduring the charging cycle. CE of Li∥Cu or Na∥Cu cells may be defined asthe amount of charge flowing out of the battery during stripping processdivided by the amount of charge entering the battery during platingprocess.

DMC: Dimethyl carbonate

DME: 1,2-Dimethoxyethane

EC: Ethylene carbonate

Electrolyte: A substance containing free ions that behaves as anionically conductive medium. Electrolytes generally comprise ions in asolution, but molten electrolytes and solid electrolytes also are known.

FEC: Fluoroethylene carbonate

Flame retardant: As used herein, the term “flame retardant” refers to anagent that, when incorporated into an electrolyte in a sufficientamount, renders the electrolyte nonflammable or flame retarded asdefined herein.

Flammable: The term “flammable” refers to a material that will igniteeasily and burn rapidly. As used herein, the term “nonflammable” meansthat an electrolyte, will not ignite or burn during operation of anelectrochemical device including the electrolyte. As used herein, theterms “flame retarded” and “low flammability” are interchangeable andmean that a portion of the electrolyte may ignite under some conditions,but that any resulting ignition will not propagate throughout theelectrolyte. Flammability can be measured by determining theself-extinguishing time (SET) of the electrolyte. The SET is determinedby a modified Underwriters Laboratories test standard 94 HB. Anelectrolyte is immobilized on an inert ball wick cut from glass fibers,such as a ball wick having a diameter of 0.3-0.5 cm, which is capable ofabsorbing 0.05-1 g electrolyte. The wick is then ignited, and the timefor the flame to extinguish is recorded. The time is normalized againstthe sample weight. If the electrolyte does not catch flame, the SET iszero and the electrolyte is nonflammable. Electrolytes having an SET of<6 s/g are also considered nonflammable. If the SET is >20 s/g, theelectrolyte is considered to be flammable. When the SET is between 6-20s/g, the electrolyte is considered to be flame retarded or have lowflammability.

Fluorinated orthoformate: A fluorinated compound having a generalformula

wherein at least one of R, R′, and R″ is fluoroalkyl and the other twosubstituents are independently fluoroalkyl or alkyl. The alkyl chainsmay be linear or branched. R, R′, and R″ may be the same or may bedifferent from one another. One or more of R, R′, and R″ may beperfluorinated.

Fluoroalkyl: An alkyl group wherein at least one H atom has beenreplaced by a F atom. A perfluoroalkyl group is an alkyl group in whichall H atoms have been replaced by F atoms.

Fluoroalkyl ether (hydrofluoroether, HFE): As used herein, the termsfluoroalkyl ether and HFE refer to a fluorinated ether having a generalformula R—O—R′, wherein one of R and R′ is fluoroalkyl and the other ofR and R′ is fluoroalkyl or alkyl. The fluoroalkyl or alkyl chain may belinear or branched. The ether may be partially fluorinated orperfluorinated where each of R and R′ is perfluoroalkyl or partiallyfluorinated alkyl. R and R′ may be the same or may be different from oneanother.

Graphite-based anode/negative electrode: A majority of the total anodemass is graphite, such as at least 70 wt %, at least 80 wt %, or atleast 90 wt % graphite.

Graphite- and silicon-based anode/negative electrode: A majority of thetotal anode mass is graphite and silicon, such as at least 70 wt %, atleast 80 wt %, or at least 90 wt % graphite and silicon.

LiBETI: lithium bis(pentafluoroethylsulfonyl)imide

LiDFOB: lithium difluoro(oxalate)borate

LiFSI: lithium bis(fluorosulfonyl)imide

LiFTFSI: lithium (fluorosulfonyl)(trifluoromethylsulfonyl)imide

LiPF₆: lithium hexafluorophosphate

LiTDI: lithium 2-trifluoromethyl-4,5-dicyanoimidazole

LiTf: lithium trifluoromethanesulfonate

LiTFSI: lithium bis(trifluoromethylsulfonyl)imide

Localized superconcentrated electrolyte (LSE) or localizedhigh-concentration electrolyte (LHCE): As used herein, the terms LSE andLHCE may be used interchangeably and refer to an electrolyte including alithium salt, a solvent in which the lithium salt is soluble, and adiluent in which the lithium salt is insoluble or poorly soluble. Thelithium ions remain associated with solvent molecules after addition ofthe diluent. The anions are also in proximity to, or associated with,the lithium ions. Thus, localized regions of solvent-cation-anionaggregates are formed. In contrast, the lithium ions and anions are notassociated with the diluent molecules, which remain free in thesolution. There are few to no free solvent molecules (i.e., most or allsolvent molecules are coordinated by lithium salt) in the dilutedelectrolyte, thereby providing the benefits of a conventionalhigh-concentration electrolyte (e.g., an electrolyte with a saltconcentration of at least 3 mol/L or M, molarity) without the associateddisadvantages.

Negative electrode: An electrode having a negative potential duringcharge and discharge of a battery or electrolytic cell.

OTE: 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether Positiveelectrode: An electrode having a positive potential during charge anddischarge of a battery or electrolytic cell.

Silicon-based anode: A majority of the total anode mass is silicon, suchas at least 70 wt %, at least 80 wt %, or at least 90 wt % silicon.

Solid electrolyte interphase (SEI) layer: A passivation layer comprisingelectrolyte decomposition products formed on the anode of lithium-ionbatteries during the first few cycles.

Soluble: Capable of becoming molecularly or ionically dispersed in asolvent to form a homogeneous solution.

TEPa: triethyl phosphate

TFEO: tris(2,2,2-trifluoroethyl) orthoformate

TMPa: trimethyl phosphate

TMS: tetramethylene sulfone

TTE: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether

VC: Vinylene carbonate

II. Electrolytes

A conventional high-concentration electrolyte (HCE) comprises a solventand a salt with a salt concentration of at least 3 M. Some HCEs have asalt concentration of at least 4 M or at least 5 M. In certaininstances, the salt molality may be up to 20 m (molality) or more, e.g.,aqueous LiTFSI. FIG. 1A is a schematic illustration of a conventionalHCE comprising a solvent and a lithium salt. Desirably, all or a largemajority of the solvent molecules are coordinated with a lithium cationin the HCE. A reduced presence or absence of free, non-coordinatedsolvent molecules may increase Coulombic efficiency (CE) of a lithiummetal anode and/or reversible insertion of Li-ions into a carbon- (e.g.,graphite and/or hard carbon) and/or silicon-based anode, facilitateformation of a stabilized solid electrolyte interphase (SEI) layer,and/or increase cycling stability of a battery including theelectrolyte. However, HCEs have disadvantages, such as high materialcost, high viscosity, and/or poor wetting of battery separators and/orelectrodes. While dilution with additional solvent can resolve one ormore of the disadvantages, dilution results in free solvent moleculesand often decreases CE, hinders formation of the stabilized SEI layer,and/or decreases cycling stability of a battery.

FIG. 1B is a schematic illustration of an exemplary “localizedhigh-concentration electrolyte” (LHCE). An LHCE includes a lithium salt,a solvent in which the lithium salt is soluble, and a diluent in whichthe lithium salt is insoluble or poorly soluble. In some embodiments,the term “soluble” means that the lithium salt has a solubility in thesolvent of at least 1 mol/L or at least 1 mol/kg. As shown in FIG. 1B,the lithium ions remain coordinated with solvent molecules afteraddition of the diluent. The anions are also in proximity to, orcoordinated with, the lithium ions. Thus, localized regions ofsolvent-cation-anion aggregates are formed. In contrast, the lithiumions and anions are not associated with the diluent molecules, whichremain free in the solution. Evidence of this electrolyte structure withregions of locally concentrated salt/solvent and free diluent moleculesis seen by Raman spectroscopy (e.g., as shown in US 2018/0251681 A1,which is incorporated by reference herein), nuclear magnetic resonance(NMR) characterization, and molecular dynamics (MD) simulations. Thus,although the solution as a whole is less concentrated than the solutionof FIG. 1A, there are localized regions of high concentration where thelithium cations are coordinated with the solvent molecules. There arefew to no free solvent molecules in the diluted electrolyte, therebyproviding the benefits of an HCE without the associated disadvantages.

Conventional electrolytes and conventional HCEs often provide onlyrelatively short cycle life in battery systems with anodes comprisingsilicon. In some instances, the compatibility of the electrolyte and thesilicon-containing anode depends at least in part on the composition ofa binder present in the anode. However, certain embodiments of thedisclosed LHCEs can resolve some or all of the problems discussed above.In addition to being compatible with silicon-containing anodes,including carbon/silicon composite-based anodes, some embodiments of thedisclosed LHCEs also are compatible with carbon-based anodes, such asgraphite anodes.

Embodiments of an LHCE as disclosed herein comprise a lithium salt, anonaqueous solvent in which the lithium salt is soluble, a diluent,wherein the lithium salt has a solubility in the diluent at least 10times less than a solubility of the lithium salt in the solvent, and anadditive having a different composition than the lithium salt, adifferent composition than the solvent, and a different composition thanthe diluent. The nonaqueous solvent comprises at least one of thefollowing components: (i) an ester, (ii) a sulfur-containing solvent,(iii) a phosphorus-containing solvent, (iv) an ether, (v) a nitrile, orany combination thereof. In some embodiments, the nonaqueous solventcomprises at least one of the following components (i) a carbonate otherthan ethylene carbonate (EC), vinylene carbonate (VC), or fluoroethylenecarbonate (FEC), (ii) a sulfone, (iii) a flame retardant comprising aphosphorus-containing solvent, (iv) an ether, or any combinationthereof. The diluent comprises a fluoroalkyl ether, a fluorinatedorthoformate, a fluorinated carbonate, a fluorinated borate, or acombination thereof. In some embodiments, the diluent comprises afluoroalkyl ether, a fluorinated orthoformate, or a combination thereof.The LHCE has a lithium salt-solvent-additive-diluent molar ratio of1:x:y:z where 0.5≤x≤5, 0≤y≤1, and 0.5≤z≤5. In some embodiments, the LHCEhas a lithium salt-solvent-additive-diluent molar ratio of 1:x:y:z where0.5≤x≤3, 0≤y≤1, and 1≤z≤5.

The solubility of the lithium salt in the solvent (in the absence ofdiluent) may be greater than 3 M, such as at least 4 M or at least 5 M.In some embodiments, the solubility and/or concentration of the lithiumsalt in the solvent is from 3 M to 10 M, such as from 3 M to 8 M, from 4M to 8 M, or from 5 M to 8 M. In certain embodiments, the concentrationmay be expressed in terms of molality and the concentration of thelithium salt in the solvent in the absence of diluent) may be from 3 mto 25 m, such as from 5 m to 21 m, or 10 m to 21 m. In contrast, themolar or molal concentration of the lithium salt in the electrolyte as awhole (salt, solvent, diluent, and additive) may be at least 20% lessthan the molar or molal concentration of the lithium salt in thesolvent, such as at least 30% less, at least 40% less, at least 50%less, at least 60% less, or even at least 70% less than the molar ormolal concentration of the lithium salt in the solvent. For example, themolar or molal concentration of the lithium salt in the electrolyte maybe 20-80% less, 20-70% less, 30-70% less, or 30-50% less than the molaror molal concentration of the lithium salt in the solvent. In someembodiments, the molar concentration of the lithium salt in theelectrolyte is within a range of 0.5 M to 6 M, 0.5 M to 3 M, 0.5 M to 2M, 0.75 M to 2 M, or 0.75 M to 1.5 M.

The lithium salt, or combination of lithium salts, participates in thecharge and discharge processes of a cell including the electrolyte.Exemplary lithium salts include, but are not limited to, compriseslithium bis(fluorosulfonyl)imide (LiFSI), lithiumbis(trifluoromethanesulfonyl)imide (LiTFSI), lithium(fluorosulfonyl)(trifluoromethylsulfonyl)imide (LiFTFSI), lithiumbis(pentafluoroethanesulfonyl)imide (LiBETI), lithiumtrifluoromethanesulfonate (LiTf), lithium bis(oxalato)borate (LiBOB),LiPF₆, LiAsF₆, LiBF₄, LiCF₃SO₃, LiClO₄, lithium difluoro(oxalato)borate(LiDFOB), LiI, LiBr, LiCl, LiSCN, LiNO₃, LiNO₂, Li₂SO₄, and combinationsthereof. In some embodiments, the salt is LiFSI, LiTFSI, LiBETI,LiTFTSI, LiTf, or a combination thereof. In certain examples, the saltis LiFSI.

The solvent associates with (e.g., solvates or coordinates) lithiumcations. When prepared as an HCE comprising the lithium salt and thesolvent, solvent-cation-anion aggregates form. Some embodiments of thedisclosed HCEs are stable toward anodes (e.g., a carbon- and/orsilicon-based anode), cathodes (including ion intercalation andconversion compounds), and/or current collectors [e.g., copper (Cu),aluminum (Al)] that may be unstable when lower concentrationelectrolytes are used and/or when other solvents are used.

The solvent is a nonaqueous solvent comprising at least one of thefollowing components: (i) an ester, (ii) a sulfur-containing solvent,(iii) a phosphorus-containing solvent, (iv) an ether, (v) a nitrile, orany combination thereof, wherein the lithium salt is soluble in thesolvent. In some embodiments, the solvent consists essentially of, orconsists of the ester, the sulfone, the phosphorus-containing solvent,the ether, or any combination thereof. The term “consists essentiallyof” means that the solvent does not include solvents, other than thoselisted, in any appreciable amount (e.g., >1 wt %). In some embodiments,the nonaqueous solvent comprises at least one of the followingcomponents (i) a carbonate other than EC, VC, or FEC, (ii) a sulfone,(iii) a flame retardant comprising a phosphorus-containing solvent, (iv)an ether, or any combination thereof.

Suitable ester solvents include, but are not limited to, carbonatesolvents and carboxylate solvents. Suitable carbonate solvents include,but are not limited to, dimethyl carbonate (DMC), ethyl methyl carbonate(EMC), diethyl carbonate (DEC), ethylene carbonate (EC), propylenecarbonate (PC), difluoroethylene carbonate (DFEC), trifluoroethylenecarbonate (TFEC), trifluoropropylene carbonate (TFPC), methyl2,2,2-trifluoroethyl carbonate (MFEC), and combinations thereof. In someembodiments, the nonaqueous solvent comprises, consists essentially of,or consists of DMC. Suitable carboxylate solvents include, but are notlimited to, ethyl acetate, ethyl propionate, methyl butyrate, ethyltrifluoroacetate, 2,2,2-trifluoroethyl acetate, 2,2,2-trifluoroethyltrifluoroacetate.

Suitable sulfur-containing solvents include, but are not limited to,sulfone solvents and sulfoxide solvents. Suitable sulfone solventsinclude, but are not limited to, dimethyl sulfone (DMS), ethyl methylsulfone (EMS), ethyl vinyl sulfone (EVS), tetramethylene sulfone (TMS,also called sulfolane). Suitable sulfoxide solvents include, but are notlimited to, dimethyl sulfoxide and ethyl methyl sulfoxide. In someembodiments, the nonaqueous solvent comprises, consists essentially of,or consists of TMS.

Suitable phosphorus-containing compounds include, but are not limitedto, organophosphorus compounds (e.g., organic phosphates, phosphites,phosphonates, phosphoramides), phosphazenes, or any combination thereof.Phosphorus-containing compounds are normally flame retardant. Organicphosphates, phosphites, phosphonates, phosphoramides include substitutedand unsubstituted aliphatic and aryl phosphates, phosphites,phosphonates, and phosphoramides. The phosphazenes may be organic orinorganic. Exemplary phosphorus-containing compounds include, e.g.,trimethyl phosphate (TMPa), triethyl phosphate (TEPa), tributylphosphate, triphenyl phosphate, tris(2,2,2-trifluoroethyl) phosphate,bis(2,2,2-trifluoroethyl) methyl phosphate, trimethyl phosphite,triphenyl phosphite, tris(2,2,2-trifluoroethyl) phosphite, dimethylmethylphosphonate, diethyl ethylphosphonate, diethyl phenylphosphonate,bis(2,2,2-trifluoroethyl) methylphosphonate, hexamethylphosphoramide,hexamethoxyphosphazene (cyclo-tris(dimethoxyphosphonitrile),hexamethoxycyclotriphosphazene), hexafluorophosphazene(hexafluorocyclotriphosphazene), and combinations thereof. In someembodiments, the nonaqueous solvent comprises, consists essentially of,or consists of TMPa, TEPa, or a combination thereof.

Suitable ether solvents include, but are not limited to,1,2-dimethoxyethane (DME), diethylene glycol dimethyl ether (DEGDME, ordiglyme), triethylene glycol dimethyl ether (triglyme), tetraethyleneglycol dimethyl ether (tetraglyme), 1,3-dioxolane (DOL), allyl ether,and combinations thereof. In some embodiments, the nonaqueous solventcomprises, consists essentially of, or consists of DME.

Suitable nitrile solvents include, but are not limited to, acetonitrile,propionitrile, succinonitrile.

The diluent comprises a fluoroalkyl ether, a fluorinated orthoformate, afluorinated carbonate, a fluorinated borate, or a combination thereof.In some embodiments, the diluent comprises a fluoroalkyl ether, afluorinated orthoformate, or a combination thereof. The lithium salt hasa solubility in the diluent at least 10 times less than a solubility ofthe lithium salt in the solvent. For instance, if the salt has asolubility of 5 M in the solvent, the diluent is selected such that thesalt has a solubility of less than 0.5 M in the diluent. In someembodiments, the lithium salt has a solubility in the solvent that is atleast 10 times, at least 15 times, at least 20 times, at least 25 times,at least 30 times, at least 40 times, or at least 50 times greater thanthe salt's solubility in the diluent. The diluent is selected to bestable with the anode, cathode, and current collectors at low lithiumsalt concentrations (e.g., 3 M) or even without the lithium salt. Insome embodiments, the diluent is selected to have a low dielectricconstant (e.g., a relative dielectric constant 7) and/or low donornumber (e.g., a donor number 10). Advantageously, the diluent does notdisrupt the solvation structure of solvent-cation-anion aggregates andis considered inert because it is not interacting with the lithium salt.In other words, there is no significant coordination or associationbetween the diluent molecules and the lithium cations. The lithiumcations remain associated with solvent molecules. Thus, although theelectrolyte is diluted, there are few or no free solvent molecules inthe electrolyte.

In any of the foregoing or following embodiments, the diluent may be afluorinated solvent having a wide electrochemical stability window(e.g., >4.5 V), such as a hydrofluoroether (HFE) (also referred to as afluoroalkyl ether) or fluorinated orthoformate. HFEs advantageously havelow dielectric constants, low donor numbers, reductive stability withthe metal of the active salt (e.g., lithium, sodium, potassium, and/ormagnesium), and/or high stability against oxidation due to theelectron-withdrawing fluorine atoms. Exemplary diluents include, but arenot limited to, 1,1,2,2-tetrafluoroethyl-2,2,2,3-tetrafluoropropyl ether(TTE), bis(2,2,2-trifluoroethyl) ether (BTFE),1,1,2,2,-tetrafluoroethyl-2,2,2-trifluoroethylether (TFTFE),1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether (OTE),1,2,2,2-tetrafluoroethyl trifluoromethyl ether, heptafluoroisopropylmethyl ether, methoxynonafluorobutane (MOFB), ethoxynonafluorobutane(EOFB), tris(2,2,2-trifluoroethyl) orthoformate (TFEO),tris(hexafluoroisopropyl) orthoformate (THFiPO), tris(2,2-difluoroethyl)orthoformate (TDFEO), bis(2,2,2-trifluoroethyl) methyl orthoformate(BTFEMO), tris(2,2,3,3,3-pentafluoropropyl) orthoformate (TPFPO),tris(2,2,3,3-tetrafuoropropyl) orthoformate (TTPO),bis(2,2,2-trifluoroethyl) carbonate, tris(2,2,2-trifluoroethyl) borate,and combinations thereof.

Exemplary flammable fluoroalkyl ethers:

Exemplary nonflammable fluoroalkyl ethers:

Exemplary fluorinated orthoformates:

The diluent may be flammable or nonflammable. In some embodiments,selecting a nonflammable diluent, such as a nonflammable fluoroalkylether or fluorinated orthoformate, significantly improves safety ofpractical rechargeable batteries. In certain embodiments, a flammablediluent may be used when the solvent comprises a flame retardant, suchas a phosphorus-containing solvent, in an amount sufficient to renderthe electrolyte flame retarded or nonflammable. In other embodiments, aflammable diluent may be used when the expected operating conditions ofthe system are relatively nonhazardous (e.g., a relatively low operatingtemperature). In some embodiments, the diluent comprises, consistsessentially of, or consists of TTE, BTFE, OTE, 1,2,2,2-tetrafluoroethyltrifluoromethyl ether, heptafluoroisopropyl methyl ether, TFEO,bis(2,2,2-trifluoroethyl carbonate), tris(2,2,2-trifluoroethyl) borate,or any combination thereof. In some embodiments, the diluent comprises,consists essentially of, or consists of TTE, BTFE, OTE, TFEO, or anycombination thereof. In certain examples, the diluent is TTE.

In some embodiments of the disclosed LHCEs, at least 90%, at least 95%,at least 96%, at least 97%, at least 98%, or at least 99% of themolecules of the solvent are coordinated with lithium cations. Incertain embodiments, fewer than 10%, such as fewer than 5%, fewer than4%, fewer than 3%, or fewer than 2% of the diluent molecules areassociated with lithium cations. The degree of coordination can bequantified by any suitable means, such as by calculating the peakintensity ratio of solvent molecules associated with cations and freesolvent in Raman spectra or by using NMR spectra.

Embodiment of the disclosed LHCEs further comprise an additive. Theadditive has a different composition than the lithium salt, a differentcomposition than the solvent, and a different composition than thediluent. In some embodiments, the additive comprises a carbonate, anether, a sulfite, a sultone (sulfonate ester), a lithium salt, aphosphate, a phosphite, a phosphine, a nitrile, a dioxazolone. Exemplaryadditives include, but are not limited to, EC (if not used as asolvent), FEC, VC, 4-vinyl-1,3-dioxolan-2-one (vinyl ethylene carbonate,VEC), 4-methylene-1,3-dioxolan-2-one (methylene ethylene carbonate,MEC), 4,5-dimethylene-1,3-dioxolan-2-one (dimethylene ethylenecarbonate, DMEC), 1,3,2-dioxathiolan-2-oxide, prop-1-ene-1,3-sultone(PES), 1-methylsulfonylethene (methyl vinyl sulfone, MVS),1-ethenylsulfonylethene (ethyl vinyl sulfone, EVS),1,3,2-dioxathiolane-2,2-dioxide, 1,3,2-dioxathiane 2,2-dioxide (DTD),lithium 2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI), lithiumbis(oxalato)borate (LiBOB), lithium difluoro(oxalate)borate (LiDFOB),lithium hexafluorophosphate (LiPF₆), 3-methyl-1,4,2-dioxazol-5-one(MDO), tris(2,2,2-trifluoroethyl) phosphite) (TTFEPi),2-oxo-1,3,2-dioxathiane (1,3-propylene sulfite, PS), hexanedinitrile(adiponitrile), butanedinitrile (succinonitrile), pentanedinitrile(glutaronitrile), tris(pentafluorophenyl) phosphine (TPFP). In someembodiments, the additive comprises EC, FEC, VC, or a combinationthereof.

The relative amounts of the salt, solvent, diluent, and additive areselected to reduce the cost of materials for the electrolyte, reduceviscosity of the electrolyte, maintain stability of the electrolyteagainst oxidation at high-voltage cathodes, improve ionic conductivityof the electrolyte, improve wetting ability of the electrolyte (e.g.,towards polyolefin separators and electrodes), facilitate formation ofan effective SEI layer, or any combination thereof. In general, theelectrolyte has a lithium salt-solvent-additive-diluent molar ratio of1:x:y:z where 0.5≤x≤5, 0≤y≤1, and 0.5≤z≤5. In some embodiments,0.5≤z≤x≤3.5, 0≤y≤1, and 1≤z≤5. In certain embodiments, x=0.5-3,y=0.01-0.5, and z=2-4. In some implementations, x=1-2, y=0.1-0.5, andz=2-4. In one embodiment, 0.5<x+y≤4.5. In an independent embodiment,0.5<x+y≤4. In another independent embodiment, 1.2≤x+y≤2.5. In stillanother independent embodiment, 0.5≤x+y≤0.65 or 1.45≤x+y≤4.5. In yetanother independent embodiment, x=0.5-3.5, y=0.01-0.8, and z=1-4. Inanother independent embodiment, x=1.5-3.0, y=0.01-0.8, and z=2-4. Instill another independent embodiment, y=0.15-0.25 and/or x+y=2-3. In yetanother embodiment, x=1.6-2.8, y=0.2-0.6, and z=3.

In one embodiment, if the diluent comprises a fluoroalkyl ether and theadditive comprises a carbonate, a sulfone, a flame retardant, an ether,or a lithium salt, then x+y is not within a range of from 0.8-1.2, orx+y is not within a range of from 0.7-1.4 or x+y is not within a rangeof from 0.67-1.43. In an independent embodiment, if the diluentcomprises a fluoroalkyl ether, then x+y is not within a range of from0.8-1.2, or x+y is not within a range of from 0.7-1.4 or x+y is notwithin a range of from 0.67-1.43. In yet another independent embodiment,if the diluent comprises1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), then0.5≤x+y≤0.58 or 1.2≤x+y≤4.5 or 1.4≤x+y≤4.5 or 0.1.45≤x+y≤4.5.

In any of the foregoing or following embodiments, the electrolyte mayhave a lithium salt to solvent molar ratio within a range of 0.4 to 0.7,such as 0.4-0.6 or 0.4-0.5. In any of the foregoing or followingembodiments, the electrolyte may have a salt molar concentration of 0.8M to 1.5 M, such as 1 M to 1.4 M. In any of the foregoing or followingembodiments, the electrolyte may have a solvent to diluent molar ratiowithin a range of 0.3 to 5, such as 0.3-2, 0.3-1, or 0.4-0.6.

In any of the foregoing or following embodiments, the additive maycomprise EC, FEC, VC, or a combination thereof, and/or y may be 0.1-0.5,such as 0.1-0.3. In any of the foregoing or following embodiments, thesolvent may comprise a carbonate other than EC, FEC, or VC, and theadditive may comprise 2 wt % to 10 wt % FEC and 0.1 wt % to 2 wt % VC.In some embodiments, FEC and VC are present in a ratio of 5:1 by weight.In certain embodiment, the electrolyte comprises 4 wt % to 6 wt % FECand 0.8 wt % to 1.2 wt % VC. In some examples, the electrolyte comprises5 wt % FEC and 1 wt % VC.

In any of the foregoing or following embodiments, the lithium salt maycomprise, consist essentially of, or consist of LiFSI. In any of theforegoing or following embodiments, the nonaqueous solvent may comprise,consist essentially of, or consist of DMC, DME, TMS, TMPa, TEPa, or anycombination thereof. In any of the foregoing or following embodiments,the diluent may comprise, consist essentially of, or consist of TTE,BTFE, OTE, TFEO, or any combination thereof. In any of the foregoing orfollowing embodiments, the additive may comprise, consist essentiallyof, or consist of EC, FEC, VC, or any combination thereof. In someembodiments, the salt comprises, consists essentially of, or consists ofLiFSI and the diluent comprises, consists essentially of, or consists ofTTE.

Advantageously embodiments of the disclosed electrolytes may be morestable toward carbon-based, silicon-based, and/or carbon/siliconcomposite-based anodes than conventional electrolytes or HCEs having asalt concentration of at least 3 M The electrolytes also may be morestable toward nickel-rich cathodes, such as LiNi_(x)Mn_(y)Co_(1−x−y)O₂(NMC) cathode materials with x≥0.8. Stability may be evidenced bycycling life, discharge capacity, capacity retention, and/or Coulombicefficiency, among other measures, as discussed in more detail below. Insome embodiments, the electrolytes may exhibit lower viscosity and/orhigher conductivity compared to HCEs. Some embodiments of the disclosedelectrolytes are useful over a wide temperature range, such as atemperature range from −30° C. to 60° C.

III. Battery Systems

Embodiments of the disclosed LHCEs are useful in battery systems, suchas rechargeable batteries. In some embodiments, the disclosed LHCEs areuseful in lithium ion batteries. In some embodiments, a system comprisesan LHCE as disclosed herein and an anode. The system may furthercomprise a cathode, a separator, an anode current collector, a cathodecurrent collector, or any combination thereof. In certain embodiments,the anode is a carbon-based (e.g., graphite-based) anode, asilicon-based anode, or a carbon- and silicon-based anode. In someexamples, the cathode is a cathode comprising an intercalation compoundor a conversion compound, such as a nickel-rich cathode as discussedbelow.

In some embodiments, a rechargeable battery comprises an LHCE asdisclosed herein, a cathode, an anode, and optionally a separator. FIG.2A is a schematic diagram of one exemplary embodiment of a rechargeablebattery 100 including a cathode 120, a separator 130 which is infusedwith an electrolyte (i.e., an LHCE, as disclosed herein, or aLiPF₆-organic carbonate based electrolyte or an HCE), and an anode 140.In some embodiments, the battery 100 also includes a cathode currentcollector 110 and/or an anode current collector 150.

In some embodiments the rechargeable battery is a pouch cell. FIG. 2B isa schematic side elevation view of one embodiment of a simplified pouchcell 200. The pouch cell 200 comprises an anode 210 comprising anodematerial 220 and an anode current collector 230, a cathode 240comprising cathode material 250 and a cathode current collector 260, aseparator 270, and a packaging material defining a pouch 280 enclosingthe anode 210, cathode 240, and separator 270. The pouch 280 furtherencloses an electrolyte as disclosed herein (not shown). The anodecurrent collector 230 has a protruding tab 231 that extends external tothe pouch 280, and the cathode current collector 260 has a protrudingtab 261 that extends external to the pouch 680.

The current collectors can be a metal or another conductive materialsuch as, but not limited to, nickel (Ni), Cu, Al, iron (Fe), stainlesssteel (SS), titanium (Ti), or conductive carbon materials. The currentcollector may be a foil, a foam, or a polymer substrate coated with aconductive material. Advantageously, the current collector is stable(i.e., does not corrode or react) when in contact with the anode orcathode and the electrolyte in an operating voltage window of thebattery. The anode and cathode current collectors may be omitted if theanode or cathode, respectively, are free standing, e.g., when the anodeis metal or a free-standing film comprising an intercalation material orconversion compound, and/or when the cathode is a free-standing film. By“free-standing” is meant that the film itself has sufficient structuralintegrity that the film can be positioned in the battery without asupport material.

In some embodiments, including some embodiments of a rechargeablelithium ion battery, the anode, or negative electrode, is asilicon-based, carbon-based (e.g., graphite-, hard, and/or softcarbon-based), or carbon- and silicon-based (e.g., a carbon/siliconcomposite) anode. By “carbon-based anode” is meant that a majority ofthe total anode mass is hard and/or soft carbon material, such as atleast 70 wt %, at least 80 wt %, or at least 90 wt % carbon material,e.g., graphite, hard carbon, soft carbon, or a mixture thereof. By“silicon-based anode” is meant that the anode contains a certain minimumamount of silicon, such as at least 5%, at least 30%, at least 50 wt %,at least 60 wt %, or at least 90 wt % silicon.

By “carbon/silicon composite-based anode” is meant that a majority ofthe total anode mass is carbon and silicon, such as at least 70 wt %, atleast 80 wt %, or at least 95 wt % of a combination of carbon andsilicon. In some examples, the silicon is nano-silicon, carbon coatednano-silicon, or nano-silicon coated on carbon. In some other examples,the silicon is micron sized porous Si with nano-pores or micron sizedbulk Si. For instance, the silicon may be carbon-coated nano-silicon,where the silicon is carbon-coated by chemical vapor deposition (CVD) orother approaches. In one embodiment, the silicon is a C/Si compositecomprising 10 wt % CVD carbon. In some embodiments, the anode is asilicon/graphite composite anode comprising 10-95 wt % graphite and 5-90wt % silicon. In certain embodiments, the anode is a silicon/graphitecomposite anode comprising 70-75 wt % graphite, 5-20 wt % silicon, 0-5wt % conductive carbon black, and 8-12 wt % binder. In some embodiments,the anode comprises a a C/Si composite comprising 5-55 wt % carbon, suchas 5-15 wt % carbon; the carbon may be CVD carbon. In someimplementations, the composite comprises carbon-coated nano-silicon. Incertain embodiments, the anode comprises stabilized porous siliconparticles coated with a heterogeneous layer comprising a discontinuoussilicon carbide (SiC) coating and a continuous carbon coating. Inparticular, the particles may comprise a porous silicon particlecomprising a plurality of interconnected silicon nanoparticles,interconnected silicon nanoparticles being connected to at least oneother silicon nanoparticle, and a plurality of pores defined by theinterconnected silicon nanoparticles, the pores including outwardlyopening surface pores and internal pores; a heterogeneous layercomprising a discontinuous SiC coating that is discontinuous across aportion of pore surfaces and across a portion of an outer surface of theporous silicon particle, and a continuous carbon coating that covers (i)outer surfaces of the discontinuous SiC coating and (ii) remainingportions of the pore surfaces and the outer surface of the poroussilicon particle.

The anode may further include one or more binders and/or conductiveadditives. Suitable binders include, but are not limited to,polyacrylates (e.g., lithium polyacrylate, LiPAA), polyimides (PI),polyvinyl alcohol, polyvinyl chloride, polyvinyl fluoride, ethyleneoxide polymers, polyvinylpyrrolidone, polyurethane,polytetrafluoroethylene, polyvinylidene fluoride, polyethylene,polypropylene, styrene-butadiene rubber, epoxy resin, nylon, and thelike. Suitable conductive additives include, but are not limited to,carbon black, acetylene black, Ketjen black, carbon fibers (e.g.,vapor-grown carbon fiber), metal powders or fibers (e.g., Cu, Ni, Al),and conductive polymers (e.g., polyphenylene derivatives). In someembodiments, the anode is prelithiated to at least 5% of capacity, atleast 10% of capacity, at least 20% of capacity, at least 30% capacityat least 50% of capacity, or up to 100% capacity, such as 0-50%capacity, 10-50% capacity, or 20-30% capacity. Prelithiation may beparticularly useful when a cathode with no lithium source is used.

Exemplary cathodes, or positive electrodes, for lithium ion batteriesinclude, but are not limited to, Li-rich Li_(1+w)Ni_(x)Mn_(y)Co_(Z)O₂(x+y+z+w=1, 0≤w≤0.25), LiNi_(x)Mn_(y)Co_(Z)O₂ (NMC, x+y+z=1), LiCoO₂,LiNi_(0.8)Co_(0.15)Al_(0.05) O₂ (NCA), LiNi_(0.5)Mn_(1.5)O₄ spinel,LiMn₂O₄ (LMO), LiFePO₄ (LFP), Li_(4−x)M_(x)Ti₅O₁₂ (M=Mg, Al, Ba, Sr, orTa; 0≤x≤1), MnO₂, V₂O₅, V₆O₁₃, LiV₃O₈, LiM^(C1) _(x)M^(C2) _(1−x)PO₄(M^(C1) or M^(C2)=Fe, Mn, Ni, Co, Cr, or Ti; 0≤x≤1), Li₃V_(2−x)M¹_(x)(PO₄)₃ (M¹=Cr, Co, Fe, Mg, Y, Ti, Nb, or Ce; 0≤x≤1), LiVPO₄F,LiM^(C1) _(x)M^(C2) _(1−x)O₂ ((M^(C1) and M^(C2) independently are Fe,Mn, Ni, Co, Cr, Ti, Mg, or Al; 0≤x≤1), LiM^(C1) _(x)M^(C2) _(y)M^(C3)_(1−x−y)O₂ ((M^(C1), M^(C2), and M^(C3) independently are Fe, Mn, Ni,Co, Cr, Ti, Mg, or Al; 0≤x≤1; 0≤y≤1, 0≤x+y≤1), LiMn_(2−y)X_(y)O₄ (X=Cr,Al, or Fe, 0≤y≤1), LiNi_(0.5−y)X_(y)Mn_(1.5)O₄ (X=Fe, Cr, Zn, Al, Mg,Ga, V, or Cu; 0≤y<0.5), xLi₂MnO₃.(1−x)LiM^(C1) _(y)M^(C2)M^(C3)_(1−y−z)O₂ (M^(C1), M^(C2), and M^(C3) independently are Mn, Ni, Co, Cr,Fe, or mixture thereof; x=0.3-0.5; y≤0.5; z≤0.5), Li₂M²SiO₄ (M²=Mn, Fe,or Co), Li₂M²SO₄ (M²=Mn, Fe, or Co), LiM²SO₄F (M²=Fe, Mn, or Co),Li_(2−x)(Fe_(1-y)Mn_(y))P₂O₇ (0≤x≤1; 0≤y≤1), Cr₃O₈, Cr₂O₅, acarbon/sulfur composite, or an air electrode (e.g., a carbon-basedelectrode comprising graphitic carbon and, optionally, a metal catalystsuch as Ir, Ru, Pt, Ag, or Ag/Pd). In an independent embodiment, thecathode may be a lithium conversion compound, such as Li₂O₂, Li₂O, Li₂S,or LiF. In some examples, the cathode comprises LiNi_(x)Mn_(y)Co_(z)O₂where x≥0.6 (NMC) or LiNi_(x)Mg_(y)Ti_(1−x−y)O₂ where 0.9≤x<1 (NMT;e.g., LiNi_(0.96)Mg_(0.02)Ti_(0.02)O₂).

The separator may be glass fiber, a porous polymer film (e.g.,polyethylene- or polypropylene-based material) with or without a ceramiccoating, or a composite (e.g., a porous film of inorganic particles anda binder). One exemplary polymeric separator is a Celgard© K1640polyethylene (PE) membrane. Another exemplary polymeric separator is aCelgard© 2500 polypropylene membrane. Another exemplary polymericseparator is a Celgard© 3501 surfactant-coated polypropylene membrane.The separator may be infused with an electrolyte, as disclosed herein.

In some embodiments, a battery includes a carbon-based, silicon-based,or carbon/silicon composite-based anode, a cathode suitable for alithium ion battery, a separator, and an LHCE comprising (a) a lithiumsalt, (b) a nonaqueous solvent composed of at least one of the followingcomponents: (i) an ester, (ii) a sulfur-containing solvent, (iii) aphosphorus-containing solvent, (iv) an ether, (v) a nitrile, or anycombination thereof; a diluent comprising a fluoroalkyl ether, afluorinated orthoformate, a fluorinated carbonate, a fluorinated borate,or a combination thereof, wherein the lithium salt has a solubility inthe diluent at least 10 times less than a solubility of the lithium saltin the solvent; and an additive having a different composition than thelithium salt, a different composition than the solvent, and a differentcomposition than the diluent. In some embodiments, the LHCE comprises(a) a lithium salt, (b) a nonaqueous solvent composed of at least one ofthe following components: (i) a carbonate other than ECVC, or FEC, (ii)a sulfone, (iii) a flame retardant comprising a phosphorus-containingsolvent, (iv) an ether, or (v) any combination thereof, wherein thelithium salt is soluble in the solvent, (c) a diluent comprising afluoroalkyl ether, a fluorinated orthoformate, or a combination thereof,wherein the lithium salt has a solubility in the diluent at least 10times less than a solubility of the lithium salt in the solvent, and (d)an additive having a different composition than the lithium salt, adifferent composition than the solvent, and a different composition thanthe diluent. The electrolyte has a lithium salt-solvent-additive-diluentmolar ratio of 1:x:y:z where 0.5≤x≤5, 0≤y≤1, and 0.5≤z≤5. In someimplementations, 0.5≤x≤3.5, 0≤y≤1, and 1≤z≤5. In some embodiments, thecathode comprises LiNi_(x)Mn_(y)Co_(z)O₂ (NMC) or LiM^(C1) _(x)M^(C2)_(y)M^(C3) _(1−x−y)O₂ (such as LiNi_(0.96)Mg_(0.02)Ti_(0.02)O₂ (NMT)).Advantageously, some embodiments of the disclosed lithium ion batteriesincluding an LHCE are operable at high voltages, e.g., a voltage of 4.2V or higher, such as a voltage 4.3 V. In certain embodiments, thebattery is operable at voltages up to 4.5 V, such as a voltage of2.5-4.5 V or 2.5-4.4 V. In any of the foregoing or followingembodiments, the battery may be operable over a temperature range from−30° C. to 60° C., such as −20° C. to 60° C., −10° C. to 60° C., or 0°C. to 60° C. In any of the foregoing or following embodiments, thebattery may be charged and/or discharged at a C rate from C/10 to 5C,such as rate from C/5 to 3C (in some examples, 1C corresponds to 2.8 mAcm⁻²). The battery may be charged and discharged at different rates.

In one embodiment, a lithium ion battery comprises a Si/Gr compositeanode and the electrolyte comprises LiFSI, DMC, VC, FEC, and a diluentcomprising BTFE, TTE, OTE, or any combination thereof. The cathode maybe any suitable cathode, such as an NMC cathode. In some examples, theDMC to diluent molar ratio is 03-5, such as 0.5-2, and the FEC and VCare present in a weight ratio of 4:1 to 6:1, such as a ratio of 5:1. Incertain examples, the electrolyte comprises 5 wt % FEC and 1 wt % VC.The salt:solvent molar ratio may be within a range of 0.4:1 to 0.6:1.

In an independent embodiment, a lithium ion battery comprises a graphiteanode and the electrolyte comprises LiFSI, DMC, TTE, and an additivecomprising VC, EC, or a combination thereof. The cathode may be anysuitable cathode, such as an NMC cathode. In some examples, theelectrolyte has a lithium salt-solvent-additive-diluent molar ratio of1:x:y:z where x is 1-2; y is 0.1-0.6, such as 0.1-0.3; and z is 1.5-3,such as 1.5-2.5. In certain examples, the salt has a molar concentrationof 0.8 M to 1.5 M, such as 1.3 M to 1.5 M, or 1.4 M.

In another independent embodiment, a lithium ion battery comprises agraphite anode and the electrolyte comprises LiFSI, DME, TTE, and anadditive comprising VC, EC, FEC, or any combination thereof. The cathodemay be any suitable cathode, such as an NMC cathode. In some examples,the electrolyte has a lithium salt-solvent-additive-diluent molar ratioof 1:x:y:z where x is 1-1.2, y is 0.1-0.3, and z is 2.5-3.0. In certainexamples, the salt has a molar concentration of 0.8 M to 1.5 M, such as0.8 M to 1.2 M, or 1 M. In some instances, the electrolyte has a lithiumsalt-solvent-additive-diluent molar ratio of 1:1.1:0.2:3.

In still another independent embodiment, a lithium ion battery comprisesa graphite anode and the electrolyte comprises LiFSI, DMC, TTE, and FEC.The cathode may be any suitable cathode, such as an NMC or NMT cathode.In some examples, the electrolyte has a lithiumsalt-solvent-additive-diluent molar ratio of 1:x:y:z where x is 1.5-2.5,y is 0.1-0.3, and z is 2.5-3.5. In certain examples, the salt has amolar concentration of 0.8 M to 1.5 M, such as 0.8 M to 1.2 M, or 1 M.In some instances, the electrolyte has a lithiumsalt-solvent-additive-diluent molar ratio of 1:2:0.2:3.

In yet another independent embodiment, a lithium ion battery comprises agraphite anode and the electrolyte is a low-flammability or nonflammableelectrolyte comprising LiFSI, TMPa, TTE, and an additive comprising VC,EC, FEC, or any combination thereof. The cathode may be any suitablecathode, such as an NMC cathode. In some examples, the electrolyte has alithium salt-solvent-additive-diluent molar ratio of 1:x:y:z where x is1-1.5, y is 0.1-0.3, and z is 2.5-3.5. In certain examples, the salt hasa molar concentration of 0.8 M to 1.5 M, such as 0.8 M to 1.2 M, or 1 M.In some instances, electrolyte has a lithiumsalt-solvent-additive-diluent molar ratio of 1:1.2:0.2:3.

In another independent embodiment, a lithium ion battery comprises agraphite anode and the electrolyte comprises LiFSI, TMS, TTE, and anadditive comprising VC, EC, FEC, or any combination thereof. The cathodemay be any suitable cathode, such as an NMC cathode. In some examples,the electrolyte has a lithium salt-solvent-additive-diluent molar ratioof 1:x:y:z where x is 2.5-3.5, y is 0.1-0.3, and z is 2.5-3.5. Incertain examples, the salt has a molar concentration of 0.8 M to 1.5 M,such as 0.8 M to 1.2 M, or 1 M. In some instances, the electrolyte has alithium salt-solvent-additive-diluent molar ratio of 1:2.8:0.2:3.

In still another independent embodiment, a lithium ion battery comprisesa Si/Gr composite anode and the electrolyte comprises LiFSI, DMC, TTE,and an additive comprising EC, FEC, or a combination thereof. Thecathode may be any suitable cathode, such as an NMC cathode. In someexamples, the electrolyte has a lithium salt-solvent-additive-diluentmolar ratio of 1:x:y:z where x is 1.5-2.5, y is 0.2-0.5, and z is2.5-3.5. In certain examples, the salt has a molar concentration of 0.8M to 1.5 M, such as 0.8 M to 1.2 M, or 1 M. In one instance, theelectrolyte has a lithium salt-solvent-additive-diluent molar ratio of1:2:0.2:3. In another instance, the electrolyte has a lithiumsalt-solvent-additive-diluent molar ratio of 1:1.7:0.5:3.

In yet another independent embodiment, a lithium ion battery comprises asilicon anode and the electrolyte comprises LiFSI, DMC, TTE, and anadditive comprising EC, FEC, or a combination thereof. The cathode maybe any suitable cathode, such as an NMC cathode. In some examples, theelectrolyte has a lithium salt-solvent-additive-diluent molar ratio of1:x:y:z where x is 1-2.5, y is 0.1-0.3, and z is 1.5-3. In someimplementations, x is 1-1.5, y is 0.1-0.3, and z is 1.5-2.5. In certainexamples, the salt has a molar concentration of 0.8 M to 1.5 M, such as1.3 M to 1.5 M, or 1.4 M. In one instance, the electrolyte has a lithiumsalt-solvent-additive-diluent molar ratio of 1:1.2:0.36:2.1. In anotherinstance, the electrolyte has a lithium salt-solvent-additive-diluentmolar ratio of 1:1.4:0.14:2.1.

In another independent embodiment, a lithium ion battery comprises aSi/Gr composite anode and the electrolyte comprises LiFSI, TTE, asolvent comprising DME, TMPa, or TMS, and an additive comprising EC,FEC, or a combination thereof. The cathode may be any suitable cathode,such as an NMC cathode. In some examples, the electrolyte has a lithiumsalt-solvent-additive-diluent molar ratio of 1:x:y:z where x is 1-3, yis 0.1-0.3, and z is 2.5-3.5. In certain examples, the salt has a molarconcentration of 0.8 M to 1.5 M, such as 0.8 M to 1.2 M, or 1 M. In oneinstance, the solvent comprises DME, and the electrolyte has a lithiumsalt-solvent-additive-diluent molar ratio of 1:1.1:0.2:3. In anotherinstance, the solvent comprises TMPa, and the electrolyte has a lithiumsalt-solvent-additive-diluent molar ratio of 1:1.2:0.2:3. In yet anotherinstance, the solvent comprises TMS, and the electrolyte has a lithiumsalt-solvent-additive-diluent molar ratio of 1:2.8:0.2:3.

In any of the foregoing or following embodiments, a lithium ion batterycomprising a graphite-based, silicon-based, or silicon- andgraphite-based anode, and an LHCE as disclosed herein may have aperformance equal to, or better than, a comparable lithium batteryincluding the same anode and cathode with a conventional electrolyte oran HCE having a salt concentration of at least 3 M.

For example, the lithium ion battery with the disclosed LHCE may have aspecific capacity, a Coulombic efficiency, and/or a capacity retentionequal to or greater than the comparable battery with the conventionalelectrolyte or superconcentrated electrolyte. A lithium ion battery witha disclosed LHCE also may exhibit a cycling stability as indicated bypercent capacity retention equal to, or better than that of, acomparable lithium ion battery including including the same anode andcathode with a conventional electrolyte or a superconcentratedelectrolyte. For example, a lithium ion battery with a silicon/graphitecomposite anode and a disclosed LHCE may have a capacity retention of atleast 70%, at least 75%, at least 80%, at least 85%, or even at least90% at 100 cycles, at 200 cycles, at 300 cycles, at 400 cycles, or evenat 500 cycles. The lithium ion battery may have a first cycle Coulombicefficiency of at least 50%, at least 60%, at least 70%, at least 75%, orat least 85%, and/or a third cycle CE of at least 90%, at least 95%, orat least 97%. In some embodiments, the lithium ion battery comprisingthe LHCE (or LSE) may have an average CE of at least 98%, at least 99%,or even at least 99.5% over at least 200 cycles, at least 300 cycles, atleast 400 cycles, or even at least 500 cycles. In certain examples, theaverage CE is 98-100%, 99-100%, or even 99.5-100% over at least 200cycles, at least 300 cycles, at least 400 cycles, or even at least 500cycles. In some examples, the first cycle Coulombic efficiency isimproved by using a prelithiated anode as disclosed herein. In any ofthe foregoing or following embodiments, the lithium ion battery may havea capacity of from 2 mAh/cm⁻² to 3 mAh/cm⁻² over at least 100 cycles orat least 200 cycles. In any of the foregoing or following embodiments,the lithium ion battery may have a specific discharge capacity of from150 mAh/g to 200 mAh/g, such as 170 mAh/g to 190 mAh/g, over at least100 cycles, at least 200 cycles, at least 300 cycles, or at least 400cycles over a temperature range of −20° C. to 60° C. In someembodiments, the lithium ion battery even has a specific dischargecapacity of at least 140 mAh/g at a temperature of −30° C. In any of theforegoing or following embodiments, the lithium ion battery also mayexhibit reduced swelling compared to batteries including conventionalsuperconcentrated electrolytes. In any of the foregoing or followingembodiments, the disclosed electrolyte may form a thinner and/or moreuniform SEI layer and/or CEI layer than a conventional electrolyte, aHCE, or an LHCE not including an additive as disclosed herein. Forexample, the SEI/CEI layers may have an average thickness that is 15-50%of the average thickness of an SEI/CEI layer produced by a conventionalelectrolyte.

IV. Representative Embodiments

Certain representative embodiments are exemplified in the followingparagraphs. An electrolyte, comprising: an active salt comprisinglithium cations; 2-10 wt % FEC; 0.1-2 wt % VC; a nonaqueous solventcomprising a carbonate other than fluoroethylene carbonate (FEC) orvinylene carbonate (VC), wherein the active salt is soluble in thenonaqueous solvent; and a diluent comprising a fluoroalkyl ether, afluorinated orthoformate, or a combination thereof, wherein the activesalt has a solubility in the diluent at least 10 times less than asolubility of the active salt in the nonaqueous solvent. Theelectrolyte, wherein: (i) the electrolyte has an active salt to solventmolar ratio within a range of from 0.4 to 0.7; or (ii) the electrolytehas a solvent to diluent molar ratio within a range of 0.3 to 5; or(iii) both (i) and (ii).

The electrolyte of the foregoing paragraph, wherein the active saltcomprises lithium bis(fluorosulfonyl)imide (LiFSI), lithiumbis(trifluoromethanesulfonyl)imide (LiTFSI), lithiumbis(pentafluoroethanesulfonyl)imide (LiBETI), lithium bis(oxalato)borate(LiBOB), LiPF₆, LiAsF₆, LiBF₄, LiCF₃SO₃, LiClO₄, lithium difluorooxalato borate (LiDFOB), LiI, LiBr, LiCl, LiSCN, LiNO₃, LiNO₂, Li₂SO₄,or any combination thereof.

The electrolyte of any of the foregoing paragraphs, wherein: (i) thenonaqueous solvent comprises dimethyl carbonate; or (ii) the active saltcomprises LiFSI; or (iii) both (i) and (ii).

The electrolyte of any of the foregoing paragraphs, wherein the diluentcomprises a fluoroalkyl ether. The electrolyte, wherein the fluoroalkylether comprises bis(2,2,2-trifluoroethyl) ether (BTFE),1,1,2,2-tetrafluoroethyl-2,2,2,3-tetrafluoropropyl ether (TTE),1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether (OTE), or anycombination thereof.

The electrolyte of any of the foregoing paragraphs, wherein the FEC andVC are present in a ratio of 5:1 by weight. The electrolyte of any ofthe foregoing paragraphs, wherein the electrolyte comprises: 4-6 wt %FEC; and 0.8-1.2 wt % VC.

The electrolyte of any of the foregoing paragraphs, wherein theelectrolyte comprises, consists essentially of, or consists of, LiFSI;FEC; VC; DMC; and BTFE, TTE, OTE, or any combination thereof.

An electrolyte, comprising: lithium bis(fluorosulfonyl)imide (LiFSI); anonaqueous solvent comprising a carbonate other than fluoroethylenecarbonate (FEC) or vinylene carbonate (VC), wherein the active salt issoluble in the nonaqueous solvent; 2-10 wt % FEC; 0.1-2 wt % VC; and adiluent comprising a fluoroalkyl ether, wherein a molar ratio of theLiFSI to the solvent is within a range of from 0.4 to 0.7, and a molarratio of the solvent to the diluent is within a range of 0.3 to 5.

The electrolyte of the foregoing paragraph, wherein the diluentcomprises bis(2,2,2-trifluoroethyl) ether (BTFE),1,1,2,2-tetrafluoroethyl-2,2,2,3-tetrafluoropropyl ether (TTE),1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether (OTE), or anycombination thereof.

The electrolyte of either of the foregoing paragraphs, wherein theelectrolyte comprises 4-6 wt % FEC; and 0.8-1.2 wt % VC.

The electrolyte of any of the preceding three paragraphs, comprising:LiFSI; dimethyl carbonate (DMC); 4-6 wt % FEC; 0.8-1.2 wt % VC; and thediluent comprises BTFE, TTE, OTE, or any combination thereof, wherein amolar ratio of LiFSI to DMC is within a range of 0.45 to 0.65, and amolar ratio of DMC to the diluent is within a range of 0.3 to 4.

The electrolyte of the foregoing paragraph, consisting essentially of,or consisting of, LiFSI; DMC; 5 wt % FEC, 1 wt % VC; and the diluent.

The electrolyte of any of the preceding three paragraphs, wherein: (i)the diluent is BTFE, a molar ratio of LiFSI to DMC is 0.4-0.5 and amolar ratio of DMC to BTFE is 0.5; or (ii) the diluent is, TTE, a molarratio of LiFSI to DMC is 0.4-0.5 and a molar ratio of DMC to TTE is 0.5;or (iii) the diluent is OTE, a molar ratio of LiFSI to DMC is 0.4-0.5and a molar ratio of DMC to OTE is 0.5; or (iv) the diluent is OTE, amolar ratio of LiFSI to DMC is 0.4-0.5 and a molar ratio of DMC to OTEis 0.6-0.7; or (v) wherein the diluent is OTE, a molar ratio of LiFSI toDMC is 0.0.4-0.5 and a molar ratio of DMC to OTE is 1; or (vi) thediluent is OTE, a molar ratio of LiFSI to DMC is 0.4-0.5 and a molarratio of DMC to OTE is 0.3-0.4; or (vii) the diluent is OTE, a molarratio of LiFSI to DMC is 0.6 and a molar ratio of DMC to OTE is 1; or(viii) the diluent is OTE, a molar ratio of LiFSI to DMC is 0.6 and amolar ratio of DMC to OTE is 2; or (ix) the diluent is OTE, a molarratio of LiFSI to DMC is 0.6 and a molar ratio of DMC to OTE is 4.

A lithium ion battery, comprising: an electrolyte according to any ofthe of the foregoing paragraphs; and an anode comprising silicon.

The lithium ion battery of the preceding paragraph, wherein the anodecomprises a graphite/silicon composite.

The lithium ion battery of the preceding paragraph, wherein the anodefurther comprises a lithium polyacrylate or polyimide binder.

The lithium ion battery of either of the preceding paragraphs, whereinthe silicon comprises microparticles of carbon-coated porous silicon.

The lithium ion battery of any of the foregoing paragraphs, furthercomprising a cathode.

The lithium ion battery of the foregoing paragraph, wherein the cathodecomprises Li_(1+w)Ni_(x)Mn_(y)Co_(Z)O₂ (x+y+z+w=1, 0≤w≤0.25),LiNi_(x)Mn_(y)Co_(z)O₂ (x+y+z=1), LiNi_(0.8)Co_(0.15)Al_(0.05) O₂,LiCoO₂, LiNi_(0.5)Mn_(1.5)O₄ spinel, LiMn₂O₄, LiFePO₄,Li_(4−x)M_(x)Ti₅O₁₂ (M=Mg, Al, Ba, Sr, or Ta; 0≤x≤1), MnO₂, V₂O₅, V₆O₁₃,LiV₃O₈, LiM^(C1) _(x)M^(C2) _(1−x)PO₄ (M^(C1) or M^(C2)=Fe, Mn, Ni, Co,Cr, or Ti; 0≤x≤1), Li₃V_(2−x)M¹ _(x)(PO₄)₃ (M¹=Cr, Co, Fe, Mg, Y, Ti,Nb, or Ce; 0≤x≤1), LiVPO₄F, LiM^(C1) _(x)M^(C2) _(1−x)O₂ ((M^(C1) andM^(C2) independently are Fe, Mn, Ni, Co, Cr, Ti, Mg, or Al; 0≤x≤1),LiM^(C1) _(x)M^(C2) _(y)M^(C3) _(1−x−y)O₂ ((M^(C1), M^(C2), and M^(C3)independently are Fe, Mn, Ni, Co, Cr, Ti, Mg, or Al; 0≤x≤1; 0≤y≤1;0≤x+y≤1), LiMn_(2−y)X_(y)O₄ (X=Cr, Al, or Fe, 0≤y≤1),LiNi_(0.5−y)X_(y)Mn_(1.5)O₄ (X=Fe, Cr, Zn, Al, Mg, Ga, V, or Cu;0≤y<0.5), xLi₂MnO₃.(1−x)LiM^(C1) _(y)M^(C2) _(z)M^(C3) _(1−y−z)O₂(M^(C1), M^(C2), and M^(C3) independently are Mn, Ni, Co, Cr, Fe, ormixture thereof; x=0.3-0.5; y≤0.5; z≤0.5), Li₂M²SiO₄ (M²=Mn, Fe, or Co),Li₂M²SO₄ (M²=Mn, Fe, or Co), LiM²SO₄F (M²=Fe, Mn, or Co),Li_(2−x)(Fe_(1-y)Mn_(y))P₂O (0≤x≤1; 0≤y<1), Cr₃O₈, Cr₂O₅, acarbon/sulfur composite, or an air electrode.

The lithium ion battery of any of the foregoing paragraphs, wherein thelithium ion battery has a capacity retention of at least 80% after 150cycles.

The lithium ion battery of any of the foregoing paragraphs, wherein thelithium ion battery has a coulombic efficiency of at least 99.7% after200 cycles.

An electrolyte, comprising: a lithium salt; a solvent comprising (i) acarbonate other than ethylene carbonate (EC), vinylene carbonate (VC),or fluoroethylene carbonate (FEC), (ii) a sulfone, (iii) a flameretardant, (iv) an ether, or (v) any combination thereof, wherein thelithium salt is soluble in the solvent; an additive having a differentcomposition than the lithium salt and a different composition than thesolvent; and a diluent comprising a fluoroalkyl ether, a fluorinatedorthoformate, or a combination thereof, wherein the lithium salt has asolubility in the diluent at least 10 times less than a solubility ofthe lithium salt in the solvent, the electrolyte having lithiumsalt-solvent-additive-diluent molar ratio of 1:x:y:z where 0.5≤x≤3.5,0≤y≤1, and 1≤z≤5.

The electrolyte of the foregoing paragraph, wherein if the diluentcomprises a fluoroalkyl ether and the additive comprises a carbonate, asulfone, a flame retardant, an ether, or a lithium salt, then x+y is notwithin a range of from 0.8-1.2, or x+y is not within a range of from0.7-1.4 or x+y is not within a range of from 0.67-1.43.

The electrolyte of the first paragraph wherein if the diluent comprisesa fluoroalkyl ether, then x+y is not within a range of from 0.8-1.2, orx+y is not within a range of from 0.7-1.4 or x+y is not within a rangeof from 0.67-1.43.

The electrolyte of the first paragraph, wherein if the diluent comprises1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), then0.5≤x+y≤0.58 or 1.2≤x+y≤4.5 or 1.4≤x+y≤4.5 or 1.45≤x+y≤4.5.

The electrolyte of any of the foregoing paragraphs, wherein 0.5≤x+y≤0.65or 1.45≤x+y≤4.5. The electrolyte of any of the foregoing paragraphs,wherein: 1.5≤x≤3.0; 0.1≤y≤0.8; and 2.5≤z≤3.5.

The electrolyte of any of the foregoing paragraphs, wherein 0.15≤y≤0.25.

The electrolyte of any of the foregoing paragraphs, wherein x+y=2-3.

The electrolyte of the first paragraph, wherein: 1.6≤x≤2.8; 0.2≤y≤0.6;2.2≤x+y≤3.0, or x+y=2.2, or x+y=3.0; and z=3.

The electrolyte of any of the foregoing paragraphs, wherein the lithiumsalt comprises comprising lithium bis(fluorosulfonyl)imide (LiFSI),lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithiumbis(pentafluoroethylsulfonyl)imide (LiBETI),lithium(tetrafluoroethylenedisulfonyl)azanide, lithium(fluorosulfonyl)(trifluoromethylsulfonyl)imide (LiFTFSI), lithiumtrifluoromethanesulfonate (LiTf), or any combination thereof.

The electrolyte of any of the foregoing paragraphs, wherein the solventcomprises dimethyl carbonate (DMC), 1,2-dimethoxyethane (DME),tetramethylene sulfone (TMS), trimethyl phosphate (TMPa), triethylphosphate (TEPa), or any combination thereof.

The electrolyte of any of the foregoing paragraphs, wherein the additivecomprises VC, EC, FEC, 4-methylene-1,3-dioxolan-2-one,4,5-dimethylene-1,3-dioxolan-2-one, 4-vinyl-1,3-dioxolan-2-one,prop-1-ene-1,3-sultone (PES), 1,3,2-dioxathiolane-2-oxide,1,3,2-dioxathiolane-2,2-dioxide, 1,3,2-dioxathiane-2,2-dioxide (DTD),lithium 2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI), lithiumdifluoro(oxalate)borate (LiDFOB), lithium hexafluorophosphate,3-methyl-,4,2-dixoazol-5-one (MDO), tris(2,2,2-trifluoroethyl) phosphite(TTFEPi), 2-oxo-1,3,2-dioxathiane, butanedinitrile, pentanedinitrile,hexanedinitrile, tris(pentafluorophenyl) phosphine,1-methylsulfonylethene, 1-ethenylsulfonylethane, or any combinationthereof. The electrolyte, wherein the additive comprises VC, EC, or acombination thereof.

The electrolyte of any of the foregoing paragraphs, wherein the lithiumsalt comprises LiFSI.

The electrolyte of any of the foregoing paragraphs, wherein the diluentcomprises 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether(TTE), bis(2,2,2-trifluoroethyl) ether (BTFE), 1H,1H,5H-octafluoropentyl1,1,2,2-tetrafluoroethyl ether (OTE), tris(2,2,2-trifluoroethyl)orthoformate (TFEO), or any combination thereof. The electrolyte,wherein the diluent comprises TTE.

The electrolyte of any of the foregoing paragraphs, comprising: (i)LiFSI, DMC, and TTE; or (ii) LiFSI, DMC, VC, and TTE; or (iii) LiFSI,DMC, EC, and TTE; or (iv) LiFSI, DMC, EC, VC, and TTE; or (v) LiFSI,TMS, and TTE; or (vi) LiFSI, TMS, VC, and TTE.

The electrolyte of the first paragraph, comprising: (i) LiFSI, DMC, andTTE in a molar ratio of 1:2.2:3; or (ii) LiFSI, DMC, VC, and TTE in amolar ratio of 1:2:0.2:3; or (iii) LiFSI, DMC, EC, and TTE in a molarratio of 1:2:0.2:3; or (iv) LiFSI, DMC, EC, and TTE in a molar ratio of1:1.6:0.6:3; or (v) LiFSI, DMC, EC, VC, and TTE in a molar ratio of1:1.4:0.6:3; or (vi) LiFSI, TMS, and TTE in a molar ratio of 1:3:3; or(vii) LiFSI, TMS, VC, and TTE in a molar ratio of 1:2.8:0.2:3.

A battery system, comprising: an electrolyte according to any of theforegoing paragraphs; an anode comprising graphite; and/or a cathode.The battery system, wherein the cathode comprisesLi_(1+w)Ni_(x)Mn_(y)Co_(z)O₂ (x+y+z+w=1, 0≤w≤0.25),LiNi_(x)Mn_(y)Co_(z)O₂ (x+y+z=1), LCoO₂, LiNi_(0.8)Co_(0.15)Al_(0.05)O₂, LiNi_(0.5)Mn_(1.5)O₄ spinel, LiMn₂O₄, LiFePO₄, Li_(4−x)M_(x)Ti₅O₁₂(M=Mg, Al, Ba, Sr, or Ta; 0≤x≤1), MnO₂, V₂O₅, V₆O₁₃, LiV₃O₈, LiM^(C1)_(x)M^(C2) _(1−x)PO₄ (M^(C1) or M^(C2)=Fe, Mn, Ni, Co, Cr, or Ti;0≤x≤1), Li₃V_(2−x)M¹ _(x)(PO₄)₃ (M¹=Cr, Co, Fe, Mg, Y, Ti, Nb, or Ce;0≤x≤1), LiVPO₄F, LiM^(C1) _(x)M^(C2) _(1−x)O₂ ((M^(C1) and M^(C2)independently are Fe, Mn, Ni, Co, Cr, Ti, Mg, or Al; 0≤x≤1), LiM^(C1)_(x)M^(C2) _(y)M^(C3) _(1−x−y)O₂ ((M^(C1), M^(C2), and M^(C3)independently are Fe, Mn, Ni, Co, Cr, Ti, Mg, or Al; 0≤x≤1; 0≤y≤1),LiMn_(2−y)X_(y)O₄ (X=Cr, Al, or Fe, 0≤y≤1), LiNi_(0.5−y)X_(y)Mn_(1.5)O₄(X=Fe, Cr, Zn, Al, Mg, Ga, V, or Cu; 0≤y<0.5), xLi₂MnO₃.(1−x)LiM^(C1)_(y)M^(C2)M^(C3) _(1−y−z)O₂ (M^(C1), M^(C2), and M^(C3) independentlyare Mn, Ni, Co, Cr, Fe, or mixture thereof; x=0.3-0.5; y≤0.5; z≤0.5),Li₂M²SiO₄ (M²=Mn, Fe, or Co), Li₂M²SO₄ (M²=Mn, Fe, or Co), LiM²SO₄F(M²=Fe, Mn, or Co), Li_(2−x)(Fe_(1-y)Mn_(y))P₂O₇ (0≤y≤1), Cr₃O₈, Cr₂O₅,a carbon/sulfur composite, or an air electrode. The battery system,wherein the cathode comprises LiNi_(x)Mn_(y)Co_(z)O₂ where x≥0.8.

Any of the foregoing battery systems, wherein the battery exhibits: (i)a capacity retention of at least 94% after 500 cycles at 25° C. comparedto the first cycle after three formation cycles; or (ii) an averagecoulombic efficiency of at least 98% after 500 cycles at 25° C.; or(iii) a capacity retention of at least 90% after 100 cycles at 60° C.compared to the first cycle after three formation cycles; or (iv) acapacity retention of at least 80% after 100 cycles at −30° C. comparedto the first cycle after three formation cycles; or (v) any combinationof (i), (ii), (iii), and (iv).

The battery system of any of the foregoing paragraphs, wherein: (i) thelithium salt comprises LiFS; or (ii) the solvent comprises DMC, DME,TMS, TMPa, TEPa, or any combination thereof; (iii) the additivecomprises VC, EC, or a combination thereof; or (iv) the diluentcomprises TTE, BTFE, TFEO, OTE, or any combination thereof; or (v) anycombination of (i), (ii), (iii), and (iv). The battery system, whereinthe additive comprises VC and the diluent comprises TTE.

The battery system of the foregoing paragraph, wherein 1.6 x≤2.8;0.2≤y≤0.6; and z=3.

A battery system, comprising: an anode, where the anode is agraphite-based anode, a silicon-based anode, or a graphite- andsilicon-based anode; a cathode; and an electrolyte comprising a lithiumsalt, a solvent comprising (i) a carbonate other than ethylene carbonate(EC), vinylene carbonate (VC), or fluoroethylene carbonate (FEC), (ii) asulfone, (iii) a flame retardant, (iv) an ether, or (v) any combinationthereof, wherein the lithium salt is soluble in the solvent, an additivehaving a different composition than the lithium salt and a differentcomposition than the solvent, and a diluent comprising a fluoroalkylether, a fluorinated orthoformate, or a combination thereof, wherein thelithium salt has a solubility in the diluent at least 10 times less thana solubility of the lithium salt in the solvent, the electrolyte havinga lithium salt-solvent-additive-diluent molar ratio of 1:x:y:z where0.5≤x≤3.5, 0.01≤y≤1, and 1≤z≤5.

The battery system, wherein: 0.5≤x≤3; 0.01≥y≤0.5; and 2≤z≤4. The batterysystem, wherein: 1≤x≤2; 0.1≤y≤0.5; and 2≤z≤4. The battery system,wherein 0.5<x+y≤4. The battery system, wherein 1.2≤x+y≤2.5.

The battery system of any of the foregoing paragraphs, wherein theadditive comprises ethylene carbonate (EC), fluoroethylene carbonate(FEC), vinylene carbonate (VC), or a combination thereof.

The battery system of any of the foregoing paragraphs, wherein thelithium salt comprises comprising lithium bis(fluorosulfonyl)imide(LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithiumbis(pentafluoroethylsulfonyl)imide (LiBETI),lithium(tetrafluoroethylenedisulfonyl)azanide, lithium(fluorosulfonyl)(trifluoromethylsulfonyl)imide (LiFTFSI), lithiumtrifluoromethanesulfonate (LiTf), or any combination thereof.

The battery system of any of the foregoing paragraphs, wherein thesolvent comprises 1,2-dimethoxyethane (DME), tetramethylene sulfone(TMS), trimethyl phosphate (TMPa), triethyl phosphate (TEPa), dimethylcarbonate (DMC), or any combination thereof.

The battery system of any of the foregoing paragraphs, wherein thediluent comprises 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether (TTE), bis(2,2,2-trifluoroethyl) ether (BTFE),1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether (OTE),tris(2,2,2-trifluoroethyl) orthoformate (TFEO), or any combinationthereof.

The battery system of any of the foregoing paragraphs, wherein: the saltcomprises LiFSI; the solvent comprises DME, TMS, TMPa, DMC, or anycombination thereof; the additive comprises EC, FEC, VC, or acombination thereof; and the diluent comprises TTE.

The battery system of any of the foregoing paragraphs, wherein theelectrolyte consists essentially of the salt, the solvent, the additive,and the diluent.

The battery system of any of the foregoing paragraphs, wherein theelectrolyte comprises: LiFSI, DME, EC, and TTE; or LiFSI, DME, FEC, andTTE; or LiFSI, DME, VC, and TTE; or LiFSI, TMS, EC, and TTE; or LiFSI,TMS, FEC, and TTE; or LiFSI, TMS, VC, and TTE; or LiFSI, TMPa, EC, andTTE; or LiFSI, TMPa, FEC, and TTE; or LiFSI, TMPa, VC, and TTE; orLiFSI, DMC, FEC, and TTE; or LiFSI, DMC, EC, and TTE; or LiFSI, DMC, EC,FEC, and TTE.

The battery system of any of the foregoing paragraphs, wherein the anodeis a graphite-based anode.

The battery system of the preceding paragraph, wherein the solventcomprises DME, TMS, or TMPa.

The battery system of any of the foregoing paragraphs, wherein the anodeis a silicon-based anode, and the solvent does not comprise a flameretardant.

The battery system of the preceding paragraph, wherein the solventcomprises TMS, DME, or DMC.

The battery system of any of the foregoing paragraphs, wherein thecathode comprises Li_(1+w)Ni_(x)Mn_(y)Co_(z)O₂ (x+y+z+w=1, 0≤w≤0.25),LiNi_(x)Mn_(y)Co_(z)O₂ (x+y+z=1), LiCo₂, LiNi_(0.8)Co_(0.15)Al_(0.05)O₂, LiNi_(0.5)Mn_(1.5)O₄ spinel, LiMn₂O₄, LiFePO₄, Li_(4−x)M_(x)Ti₅O₁₂(M=Mg, Al, Ba, Sr, or Ta; 0≤x≤1), MnO₂, V₂O₅, V₆O₁₃, LiV₃O₈, LiM^(C1)_(x)M^(C2) _(1−x)PO₄ (M^(C1) or M^(C2)=Fe, Mn, Ni, Co, Cr, or Ti;0≤x≤1), Li₃V_(2−x)M¹ _(x)(PO₄)₃ (M¹=Cr, Co, Fe, Mg, Y, Ti, Nb, or Ce;0≤x≤1), LiVPO₄F, LiM^(C1) _(x)M^(C2) _(1−x)O₂ ((M^(C1) and M^(C2)independently are Fe, Mn, Ni, Co, Cr, Ti, Mg, or Al; 0≤x≤1), LiM^(C1)_(x)M^(C2) _(y)M^(C3) _(1−x−y)O₂ ((M^(C1), M^(C2), and M^(C3)independently are Fe, Mn, Ni, Co, Cr, Ti, Mg, or Al; 0≤x≤1; 0≤y≤1),LiMn_(2−y)X_(y)O₄ (X=Cr, Al, or Fe, 0≤y≤1), LiNi_(0.5−y)X_(y)Mn_(1.5)O₄(X=Fe, Cr, Zn, Al, Mg, Ga, V, or Cu; 0≤y<0.5), xLi₂MnO₃.(1−x)LiM^(C1)_(y)M^(C2)M^(C3) _(1−y−z)O₂ (M^(C1), M^(C2), and M^(C3) independentlyare Mn, Ni, Co, Cr, Fe, or mixture thereof; x=0.3-0.5; y≤0.5; z≤0.5),Li₂M²SiO₄ (M²=Mn, Fe, or Co), Li₂M²SO₄ (M²=Mn, Fe, or Co), LiM²SO₄F(M²=Fe, Mn, or Co), Li_(2−x)(Fe_(1-y)Mn_(y))P₂O (0≤y≤1), Cr₃O₈, Cr₂O₅, acarbon/sulfur composite, or an air electrode. The battery system ofclaim 17, wherein the cathode comprises: LiNi_(x)Mn_(y)Co_(z)O₂ wherex≥0.6; or LiNi_(x)Mg_(y)Ti_(1−x−y)O₂ where 0.9≤x<1.

The battery system of any of the foregoing paragraphs, wherein thebattery system exhibits: (i) a first cycle coulombic efficiency of atleast 75%; or (ii) an average coulombic efficiency of at least 98% over500 cycles at 25° C. after three formation cycles; (iii) a capacityretention of at least 85% after 500 cycles at 25° C. compared to thefirst cycle after three formation cycles; or (iv) a capacity retentionof at least 90% from 350^(th) cycle to 500^(th) cycle; or (v) anycombination of (i), (ii), (iii), and (iv).

The battery system of any of the foregoing paragraphs, wherein: (i) thebattery system is capable of operating at a voltage of 4.4 V or higher;or (ii) the battery system is capable of operating over a temperaturerange of from 20° C. to 50° C.; or (iii) both (i) and (ii).

An electrolyte comprising a lithium salt, a solvent comprising (i) acarbonate other than ethylene carbonate (EC), vinylene carbonate (VC),or fluoroethylene carbonate (FEC), (ii) a sulfone, (iii) a flameretardant, (iv) an ether, or (v) any combination thereof, wherein thelithium salt is soluble in the solvent, an additive having a differentcomposition than the lithium salt and a different composition than thesolvent, and a diluent comprising a fluoroalkyl ether, a fluorinatedorthoformate, or a combination thereof, wherein the lithium salt has asolubility in the diluent at least 10 times less than a solubility ofthe lithium salt in the solvent, the electrolyte having a lithiumsalt-solvent-additive-diluent molar ratio of 1:x:y:z where 0.5≤x≤3.5,0.01≤y≤1, and 1≤z≤5.

The electrolyte of the foregoing paragraph, wherein: 0.5×3; 0.01≤y≤0.5;and 2≤z≤4. The electrolyte of the foregoing paragraph, wherein: 1×2;0.1≤y≤0.5; and 2≤z≤4. The electrolyte of the foregoing paragraph,wherein 0.5≤x+y≤4. The electrolyte of the foregoing paragraph, wherein1.25≤x+y≤2.5.

The electrolyte of any of the foregoing paragraphs, wherein the additivecomprises ethylene carbonate (EC), fluoroethylene carbonate (FEC),vinylene carbonate (VC), or a combination thereof.

The electrolyte of any of the foregoing paragraphs, wherein the lithiumsalt comprises comprising lithium bis(fluorosulfonyl)imide (LiFSI),lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithiumbis(pentafluoroethylsulfonyl)imide (LiBETI),lithium(tetrafluoroethylenedisulfonyl)azanide, lithium(fluorosulfonyl)(trifluoromethylsulfonyl)imide (LiFTFSI), lithiumtrifluoromethanesulfonate (LiTf), or any combination thereof.

The electrolyte of any of the foregoing paragraphs, wherein the solventcomprises 1,2-dimethoxyethane (DME), tetramethylene sulfone (TMS),trimethyl phosphate (TMPa), triethyl phosphate (TEPa), dimethylcarbonate (DMC), or any combination thereof.

The electrolyte of any of the foregoing paragraphs, wherein the diluentcomprises 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether(TTE), bis(2,2,2-trifluoroethyl) ether (BTFE), 1H,1H,5H-octafluoropentyl1,1,2,2-tetrafluoroethyl ether (OTE), tris(2,2,2-trifluoroethyl)orthoformate (TFEO), or any combination thereof.

The electrolyte of any of the foregoing paragraphs, wherein theelectrolyte comprises: LiFSI, DME, EC, and TTE; or LiFSI, DME, FEC, andTTE; or LiFSI, DME, VC, and TTE; or LiFSI, TMS, EC, and TTE; or LiFSI,TMS, FEC, and TTE; or LiFSI, TMS, VC, and TTE; or LiFSI, TMPa, EC, andTTE; or LiFSI, TMPa, FEC, and TTE; or LiFSI, TMPa, VC, and TTE; orLiFSI, DMC, FEC, and TTE; or LiFSI, DMC, EC, and TTE; or LiFSI, DMC, EC,FEC, and TTE.

The electrolyte of any of the foregoing paragraphs, wherein theelectrolyte consists essentially of the salt, the solvent, the additive,and the diluent.

V. Examples Example 1 DMC-Based Electrolytes for Cells with Si/GrComposite Anodes

A baseline electrolyte formula and several LHCE formulas are shown inTable 1. The baseline electrolyte was prepared on the basis of molarity,whereas the other electrolytes were prepared on the basis of molarratio. Additives, such as VC and FEC, were added after mixing thelithium salt with solvent and diluent.

TABLE 1 Formulations of the investigated electrolytes Name FormulationBaseline 1.2M LiPF₆ in EC-EMC (3:7 by wt.) + 10 wt. % FEC LaLiFSI-DMC-BTFE (molar ratio = 0.51:1.1:2.2) + 1.0 wt % VC + 5 wt % FECLb LiFSI-DMC-TTE (molar ratio = 0.51:1.1:2.2) + 1.0 wt % VC + 5 wt % FECLc1 LiFSI-DMC-OTE (molar ratio = 0.51:1.1:2.2) + 1.0 wt % VC + 5 wt %FEC Lc2 LiFSI-DMC-OTE (molar ratio = 0.51:1.1:1.65) + 1.0 wt % VC + 5 wt% FEC Lc3 LiFSI-DMC-OTE (molar ratio = 0.51:1.1:1.1) + 1.0 wt % VC + 5wt % FEC Lc4 LiFSI-DMC-OTE (molar ratio = 0.51:1.1:3.3) + 1.0 wt % VC +5 wt % FEC Lc5 LiFSI-DMC-OTE (molar ratio = 0.51:0.84:0.84) + 1.0 wt %VC + 5 wt % FEC Lc6 LiFSI-DMC-OTE (molar ratio = 0.51:0.84:0.42) + 1.0wt % VC + 5 wt % FEC Lc7 LiFSI-DMC-OTE (molar ratio = 0.51:0.84:0.21) +1.0 wt % VC + 5 wt % FEC

Full cells were prepared. The anode was composed of 88 wt % Si/Grcomposite (BTR New Energy Materials Inc.), 10 wt % polyimide (P84, HPPOLYMER GmbH) and 2 wt % carbon black (C65, Imerys) BTR. Loading levelwas 2.7 mg/cm⁻². The cathode was composed of 90 wt %Li[Ni_(0.5)Mn_(0.3)Co_(0.2)]O₂ (NMC532, Toda), 5 wt % carbon black (C45,Imerys), and 5 wt % polyvinylidene fluoride (Solef 5130, Solvay). Theloading level and electrode density of cathode were 11.4 mg/cm⁻² and 2.7g/cm³, respectively. The loading level of each anode and cathode wasadequately controlled to satisfy the N/P ratio of 1.2 in the full-cell.

Electrochemical cell testing: Before the full-cell test, the Si anodewas cycled 3 times at a C-rate of 0.1C (1C corresponds to 900 mA/g) in a2032 coin-type half-cell with Li metal as a counter electrode. Theoperation voltage window was set from 0.02 V to 1.5 V. After the Sielectrodes reached the fully delithiated state, they were collected bydisassembling the cell. Then they were paired with a cathode forfull-cell test in the 2032 coin-type cell. The full-cell was initiallycycled for 3 cycles at the C-rate of 0.05C (1C corresponds to 130 mA/g,where the weight is based on only cathode material), then further cycledat the C-rate of 0.33C (1C corresponds to 130 mA/g). The voltage windowwas between 3.0 V to 4.1 V.

FIG. 3 compares the cycling performance of Si/Gr∥NMC532 full cells usingbaseline electrolyte and La/Lb electrolytes. After formation cycles, thecapacity retention of the cell using baseline electrolyte was 80% in 200cycles. In contrast, the capacity retentions of the cells using La andLb electrolytes were 94% and 88% at 200^(th) cycles, respectively. After300 cycles, the capacity retentions of the cells using La and Lb were88% and 81%, respectively. Sample Lb-Re in FIG. 3 is the repeat ofsample Lb.

FIG. 4 compares the coulombic efficiency (CE) of Si/Gr∥NMC532 full cellsusing baseline electrolyte and La/Lb electrolytes. At the 200^(th)cycle, the CE of cells using baseline electrolyte, La and Lb were99.77%, 99.99%, and 99.95%, respectively. This trend is consistent withthe trend of the capacity retention shown in FIG. 1. Sample Lb-Re inFIG. 4 is the repeat of sample Lb.

FIG. 5 compares the cycling performance of Si/Gr∥NMC532 full cells usingbaseline electrolyte and Lc series of electrolytes. After formationcycles, the capacity retention of the cell using baseline electrolytewas 85% in 150 cycles. In contrast, the capacity retentions of the cellsusing Lc1, Lc2, Lc3, Lc4, Lc5, and Lc6 electrolytes were 87%, 89%, 91%,80%, 95% and 97% in 150 cycles, respectively. The capacity retention ofthe cell using Lc7 was 98% in 50 cycles.

FIG. 6 compares the coulombic efficiency (CE) of Si/Gr∥NMC532 full cellsusing baseline electrolyte and Lc series of electrolytes. At the200^(th) cycle, the CE of cells using baseline electrolyte, Lc1, Lc2,Lc3, Lc4, Lc5, and Lc6 electrolytes were 99.89%, 99.74%, 99.86%, and99.81%, 99.78%, 99.83%, and 99.88% respectively. This trend isconsistent with the trend of the capacity retention shown in FIG. 5.

Example 2 DMC-Based Electrolytes for Cells with Graphite AnodesExperimental:

Electrolyte and electrode preparation: The electrolytes were prepared bydissolving the LiFSI or LiPF₆ in the selected solvent and additivemixtures inside an MBraun glovebox filled with purified argon, where themoisture and oxygen content was less than 1 ppm. The NMC811 cathode(composed of 96 wt. % NMC811 as active material and with an arealcapacity loading of 2.8 mAh cm⁻²) and the Gr anode (areal capacityloading ˜3.5 mAh cm⁻²) electrode laminates. The cathode was punched into1.27 cm⁻² disks and the Gr anode was punched into 1.77 cm⁻² disks. Theelectrode disks were further dried at 120° C. overnight under vacuumbefore use.

Physical properties measurements: Electrolyte conductivities wereperformed on a Bio-Logic MCS 10 fully integrated multichannelconductivity spectroscopy in the temperature range of −40° C. to 60° C.The viscosities of the electrolytes as a function of temperature weremeasured with an Anton Paar rheometer (Ashland, Va., USA). A cone-platemeasuring system, CP25-1 coupled with a P-PTD200 cell, was used. APeltier system installed in the measuring system was employed fortemperature control. The temperature of samples was initially set at −7°C. to start the measurements. Once a measurement was started,temperature was increased linearly from −7 to 50° C. in a time durationof 32 min while the viscosity was measured and recorded, with a shearrate of 40 s⁻¹. A nitrogen flow chamber was set up above the measuringplate to minimize the sample exposure to air. A certificated viscositystandard S60 (Cannon Instrument Co., State College, Pa., USA) was usedto calibrate the rheometer measuring system.

Electrochemical tests: CR2032 coin cells (from MTI Corporation) wereassembled for electrochemical test. In Gr∥NMC811 cells, a piece of Granode disk, a piece of polyethylene separator (Asahi Hi-Pore, Japan), apiece of NMC811 cathode disk and an extra piece of Al disk weresandwiched together with 100 μL electrolyte and crimped in coin cellswith Al-clad positive cans inside the argon-filled glovebox. The cellswere cycled at C/3 charge and discharge rate after three formationcycles at C/20 with a cutoff voltage range of 2.5-4.4 V, where 1Ccorresponds to the current density of 2.8 mA cm⁻². Linear sweepvoltammetry (LSV) studies of the electrolyte solutions were conducted ina three-electrode cell configuration (Li|Li|SP-PVDF/AI, the SP arealloading was 0.5 mg cm⁻²) with a scan rate of 0.1 mV s⁻¹ using a CHI606Eworkstation. Li∥Gr half cells were performed with a cyclic voltammetry(CV) test in a cutoff voltage range of 0.01-2.0 V using scan rate of 0.1mV s⁻¹.

Characterizations: For postmortem analyses, including X-ray diffraction(XRD), scanning electron microscopy (SEM), transmission electronmicroscopy (TEM) and X-ray photoelectron spectroscopy (XPS)measurements, the cycled cells were carefully disassembled inside theglovebox to collect the cycled Gr anodes and NMC811 cathodes. Thesecycled electrodes were rinsed with pure anhydrous DMC solvent to removeresidual electrolyte, dried and then sealed in the glovebox before beingtransferred for characterizations. XRD patterns were obtained on aRigaku MiniFlex II XRD instrument (Cu Ka radiation, 30 kV, 15 mA, andscan rate 1.0° per min). SEM measurements were carried out on a Heliosfocused ion beam (FIB)-SEM at an accelerating voltage of 5 kV and acurrent of 86 pA. The TEM samples were performed on FEI Helios Dual Beamsystem. A randomly selected secondary particle of NMC811 was coated witha ˜2 μm Pt layer. The particle was then extracted along with the cappinglayers and welded to the TEM grid (Zou et al., Chem. Mater. 2018,30:7016). The FIB processes were performed at 30 kV, 5 kV and 2 kV toremove the damaged layers and polish the surface. The as-prepared samplewas characterized by a JEOL JEM-ARM2000 F spherical-aberration-correctedmicroscope with a convergence angle set at 20.6 mrad for imaging (ibid.,Li et al., Science 2017, 358:506). XPS measurements were conducted on aPhysical Electronics Quantera scanning X-ray microprobe with a focusedmonochromatic Al Ka X-ray (1,486.7 eV) source for excitation and a passenergy of 69.0 eV for high-energy-resolution spectra collection. All theXPS results were fitted with CasaXPS software. The binding energy wascalibrated by shifting the C—C/C—H peak to 284.8 eV in C 1s spectra.Shirley BG type was used for background subtraction and GL(30) lineshape was used for peak fit. The differential scanning calorimetrymeasurements were carried out in a Perkin Elmer DSC 6000 using ascanning rate of 2° C. min⁻¹ from −50° C. to 50° C.

Three exemplary LHCEs (noted as AE001-AE003, whose formulations arelisted in Table 2), based on LiFSI as the salt, organic carbonatesolvents (DMC, EC and VC) as the solvating solvent, and TTE as thediluent were developed and evaluated in the cell chemistry with astate-of-the-art high voltage NMC811 (2.8 mAh cm⁻²) cathode and acommercial Gr anode (3.5 mAh cm⁻²). These LHCEs exhibited excellentcompatibility with both Gr anode and NMC811 cathode, and effectivelygenerated thin, uniform and robust passivation films (SEI and CEI) onboth the anode and cathode surfaces to prevent the electrolytes fromcontinuous chemical/electrochemical decomposition and transition metaldissolution. Accordingly, significantly improved cycling stability ofLIBs under the high cut-off voltage of 4.4 V operating at both roomtemperature and high temperatures, good rate capability under chargingand discharging, and excellent low-temperature discharging performancewas simultaneously achieved in the LiFSI-DMC-EC LHCE. This workdemonstrated that, in some embodiments, the SEI and CEI, but not theelectrolyte conductivity and viscosity, govern the LIB performances forfast charging and discharging and low-temperature behavior, so this workrepresents a viable path to the successful utilization of fast chargingand high voltage LIBs in a wide-temperature range.

TABLE 2 Electrolyte formulation, density, conductivity, and viscosity(all at 25° C.) of the baseline electrolyte and the three LHCEs studiedin this work Density Conductivity Viscosity Electrolyte Electrolyteformulation (g ml⁻¹) (mS cm⁻¹) (cP) E-baseline 1.0M LiPF₆ in 1.39 6.073.35 EC-EMC (3:7 by wt.) + 2 wt. % VC AE001 1.4M LiFSI in 1.50 1.40 3.67DMC-TTE (2.2:3 by mol.) AE002 1.4M LiFSI in 1.55 1.05 3.53 DMC-VC-TTE(2:0.2:3 by mol.) AE003 1.4M LiFSI in 1.49 1.07 3.69 DMC-EC-TTE (2:0.2:3by mol.)

Electrochemical Stability

The formulations and basic properties of the three LHCEs (AE001-AE003)and the conventional LiPF₆/carbonate electrolyte (noted as E-baseline)are listed in Table 2. The electrochemical stabilities of the fourelectrolytes on Gr anode and at high voltages were first evaluated by CVin Li∥Gr cells and LSV in Li|Li|SP-PVDF/Al three-electrode cells,respectively. It is observed from the CV profiles in FIG. 7 that allthree LHCEs showed good compatibility with Gr anode as the baselineelectrolyte did, enabling the evaluation of these new electrolytes inGr-based LIBs. The lower response current densities for the LHCEs thanthat for E-baseline are possibly due to the lower room-temperature ionicconductivities of LHCEs (Table 2, FIG. 8A). The ionic conductivityvalues are 4-6 times lower than those of the E-baseline. For instance,the ionic conductivities at 25° C. were 1.40 mS cm⁻¹ for AE001, 1.05 mScm⁻¹ for AE002, 1.07 mS cm⁻¹ for AE003, and 6.07 mS cm⁻¹ for E-baseline.However, the viscosities of LHCEs showed larger changes with temperaturethan that of E-baseline, where a cross point occurred at about 27° C.with the viscosity value of about 3.4 cP (FIG. 8B). Above 27° C., thethree LHCEs had lower viscosities than the E-baseline; but below 27° C.the LHCEs showed larger viscosities than E-baseline.

On the high voltage side, the LSV scans in FIG. 9 showed the anodicdecomposition (with a response current density of 0.05 pA cm⁻²) on anSP-PVDF/AI electrode started at 4.70 V in AE001, 4.60 V in AE002, 4.93 Vin AE003, and 4.74 V in E-baseline. Although AE001 and AE002 showedslightly lower oxidation potential than E-baseline, the former twoelectrolytes exhibited much lower current density after 4.91 V than thecontrol electrolyte, indicating good passivation formed from the twoLHCEs. Overall, AE003 exhibited superior oxidative stability and goodcompatibility with Gr electrode, being expected to offer advancedelectrochemical performances in high voltage LIBs.

Battery Performance

The long-term cycling stability, rate capability and low-temperaturedischarge performance of the three LHCEs and the E-baseline wereinvestigated in Gr∥NMC811 coin cells under the voltages range of 2.5-4.4V after three formation cycles performed at C/20 for the first cycle andC/10 for the other two cycles, where 1C corresponds to 2.8 mAh cm⁻². Thevoltage profiles of the first formation cycle of the cells withdifferent electrolytes at 25° C. are shown in FIG. 10. The cells withthe four different electrolytes showed slightly different curves duringcharge, possibly because of the different oxidations of the electrolytecomponents, but their discharge curves were nearly the same. The cellusing AE003 showed the highest discharge capacity of 194.3 mAh g⁻¹ andalso the highest Coulombic efficiency (CE) of 80.8% at the first cycle,while the cells using other three electrolytes (AE001, AE002 andE-baseline) exhibited similar discharge capacities of 188.4, 186.8 and188.5 mAh g⁻¹, respectively and the CE values were 78.8% for AE001,79.3% for AE002 and 77.9% for E-baseline. FIG. 11A shows the long-termcycling stability of Gr∥NMC811 coin cells with the four electrolytes at25° C. under the charge/discharge rate of C/3 after three formationcycles. The corresponding cycling CE and the voltage profiles atselected cycles are shown in FIGS. 12A-12E. It was clearly observed thatalthough the cell with E-baseline electrolyte exhibited slightly higherdischarge capacities than the three LHCEs in the first 100 cycles, ithad an abrupt capacity drop after that (FIG. 11A), with capacityretentions of 71.5% and 12.5% at the 150^(th) and 200^(th) cycles,respectively (compared to the capacity of the first cycle at C/3 rateafter the three formation cycles), and a fluctuation of cycling CE after150 cycles (FIG. 12A). This can be attributed to the poorelectrode/electrolyte stability of E-baseline on both Gr and NMC811 andthe aggressive side reactions of E-baseline with the Ni-rich NMCmaterial, especially the highly reactive Ni⁴, which will be discussedlater. The consequence was the quick propagation of resistive surfacefilms on Gr and NMC811 surfaces and accordingly the increasedoverpotential (FIG. 12B), leading to the battery failure at an earlystage.

In comparison, the cells with all three LHCEs exhibited significantlyimproved cycling stability. The cells with AE001 and AE002 gavedischarge capacities of 179.8 and 172.9 mAh g⁻¹ at the 400^(th) cyclewith capacity retentions of 100% and 98.6%, respectively. After that,the cell with AE001 experienced capacity fading accompanied by CEfluctuation and voltage polarization, which were more severe after the500^(th) cycle (FIGS. 12A, 12C), resulting in a capacity retention of40.7% after 600 cycles. When part of the DMC in AE001 was replaced withVC (i.e. AE002), no capacity attenuation and slight overpotentialincrease were observed in the cell with AE002 during the 600 cycles(FIGS. 12A, 12D), but the capacity and the CE exhibited fluctuations, anirregular behavior after 400 cycles (FIGS. 11A, 12A), indicating theoccurrence of side reactions in the cell with AE002 after long-termcycling. When the VC in AE002 was replaced by equal moles of EC,significant improvement in cycling stability in terms of capacity, CEand overpotential were obtained in the cell with AE003 (FIGS. 10, 12A,12E). The discharge capacity at the 600^(th) cycle for the cell withAE003 was 173.4 mAh g⁻¹, corresponding to a capacity retention of 94.2%.Meanwhile, the CE remained at 99.9% during the 600 cycles for the cellwith AE003, much more stable than the CEs for the cells with AE001 andAE002 (FIG. 12A). This is probably because the participation of ECbenefited the formation of uniform and robust SEI on Gr and CEI onNMC811 (which will be discussed more in later sections). Moreimportantly, there was negligible increase in cell overpotential during600 cycles for the cell with AE003 (FIG. 12E), indicating that theelectrode/electrolyte interphase layers are highly conductive for Li⁺ion transportation under the participation of EC.

In the conventional LiPF₆/carbonate electrolyte, an increase in testingtemperature will drastically accelerate the parasitic reactions ofelectrolyte on both high-Ni NMC cathode and Gr anode. This willaccelerate the degeneration of NMC cathode and cause the formation ofmore resistive components in the SEI film of Gr anode, which in turnresults in fast capacity loss. The cycling performance of the Gr∥NMC811coin cells with the four electrolytes was evaluated at 60° C. afterthree formation cycles at 25° C. As seen from FIG. 11B, the cell withE-baseline exhibited a sharp capacity drop at the 35^(th) cycle and thecapacity retention after 50 cycles was only 19.4%, accompanying withobviously increased voltage polarization (FIG. 13C). In contrast, thecells with AE001-AE003 demonstrated superior high-temperature cyclingperformance with the reversible capacities of 174.3, 177.9 and 183.6 mAhg⁻¹ after 100 cycles (FIG. 11B), corresponding to capacity retentions of90.2%, 91.8% and 94.9%, respectively, with limited increase inoverpotential during the 100 cycles (FIGS. 13D-13F). As evidenced by theelectrochemical impedance spectroscopy (EIS) results of the Gr∥NMC811cells before and after 100 cycles at 60° C. shown in FIG. 14, the totalimpedances of the cells with four electrolytes were small before cyclingand the cell with E-baseline was slightly smaller than those with LHCEs.However, after 100 cycles at 60° C. the cell with E-baseline had asignificant increase in the contact resistance (R_(b)), the surface filmresistance (R_(film)) and the charge transfer resistance (R_(ct)), whilethe cells using AE001-AE003 had a slight increase in R_(b), limitedincrease in R_(film) and low values of R_(ct). The cells using AE002 andAE003 had even smaller R_(ct) than that of AE001. The values of theR_(b), R_(film) and R_(ct) were fitted according to the equivalentcircuit in FIG. 14, and the results are presented in Table 3. The EISresults confirmed the much more conductive surface films formed on theelectrode/electrolyte interfaces using AE001-AE003, especially AE002 andAE003 after cycling, even at 60° C.

TABLE 3 EIS fitting results for Gr∥NMC811 cells with differentelectrolytes. After 3 formation cycles After 100 cycles at 60° C.Electrolyte R_(b) (Ω) R_(film) (Ω) R_(ct) (Ω) R_(b) (Ω) R_(film) (Ω)R_(ct) (Ω) E-baseline 2.8 2.3 8.9 30.3 48.0 160.8 AE001 4.4 7.6 9.7 5.321.6 38.8 AE002 4.1 6.8 9.6 6.7 16.1 29.8 AE003 4.1 4.3 6.1 3.2 15.022.8

When the formation cycles of the Gr∥NMC811 coin cells were conducted atelevated temperatures (e.g. 60° C.), the three LHCEs also led to verystable cycling performance (FIG. 15B) at the same temperature as theformation cycles were conducted, with limited change in overpotential(FIGS. 15C-15F) although the cell capacities decreased with increasingthe formation temperature. The CEs of the first formation cycle usingE-baseline and AE001-AE003 all decreased to the range of 65-68% (FIG.15A). This is possibly because more parasitic electrolyte decompositionsoccurred on both Gr and NMC811 electrodes during the formation cycles atthe elevated temperature, resulting in lower first cycle CE, thickersurface film, larger resistance of the SEI layer, and more loss of Li⁺in the cathode material, thus lower capabilities of the cells (160-167mAh g⁻¹) when compared to those of cells with formation cycles performedat 25° C. On the contrary, the Gr∥NMC811 cell using the conventionalLiPF₆ electrolyte showed much inferior cycling performance (FIG. 15B).The rapid capacity drop in E-baseline occurred about 30 cycles at 60° C.and the remaining capacity was almost negligible at the 100^(th) cycle.In comparison, the capacity retentions after 100 cycles for AE001, AE002and AE003 were 98.6%, 96.5%, and 98.0%, respectively. In addition, thecell overpotential growth in AE001-AE003 was almost negligible duringthe 100 cycles, compared to the significant voltage polarization afterthe first cycle using the baseline electrolyte (FIGS. 15C-15F). It isindicated that even at higher formation temperature, the cells withthree LHEs especially AE003 demonstrated excellent cycling stability andless voltage polarization, which is also an indication of the highquality of formed SEI on Gr and CEI on NMC811 at elevated temperatures.

The rate capabilities of the three LHCEs and the E-baseline at differentC rates were also evaluated in Gr∥NMC811 cells by two testing protocols.Under the protocol with a constant charge rate of C/5 and differentdischarge rates from C/5 to 5C, as shown in FIG. 16A, the cell withAE003 showed the superior discharge rate capability in the full raterange while the baseline electrolyte suffered rapid capacity fading whendischarge rates were 3C and 5C. The cells with AE001 and AE002 exhibitedsimilar discharge rate capability like E-baseline at 1C rate and belowbut better performance than E-baseline at discharge rates of 3C and 5C.When the discharge rate was changed back to C/5, the cells with all fourelectrolytes had the similar discharge capacities. As for the protocolwith different charge rates from C/5 to 5C but the same discharge rateof C/5 (FIG. 16B), the cell with AE002 showed inferior rate capabilitythan the cells with other LHCEs and the baseline electrolyte from C/5 to5C. The cell with AE001 kept similar reversible capacities like the cellwith E-baseline when the charge rate was up to 2C, and the cell withAE003 maintained the same rate capability as the cell with E-baselinetill 3C rate during charging. When the charge rate was increased to 5C,the cells with all three LHCEs showed very limited capacity, lower thanthe cell with E-baseline. This is mainly because the LHCEs have strongerion associations (FIG. 17) than the baseline electrolyte, which makes itmore difficult to de-solvate at the SEI of the Gr electrode. When VC andEC were added in the LHCEs (i.e. AE002 and AE003), even stronger ionassociations occurred compared to the LHCE AE001 with only DMC as thesolvating solvent. However, when the charge rate was set back to C/5,the recovering discharge capacity from high to low followed the order ofAE003>>AE002>AE001>>E-baseline. The results from both rate capabilitytesting protocols demonstrated the superior rate performance of thecells with AE003 up to 3C rate, indicating the more conductiveelectrode/electrolyte interfaces on both Gr and NMC811 electrodes andcorrespondingly fast electrode redox reaction kinetics in the cells withAE003.

Furthermore, the low-temperature discharging performance of the LHCEsand E-baseline was performed (25° C. to −40° C.), as shown in FIGS. 18and 19A-19D. Even with much lower ionic conductivities and doubledviscosities under low temperatures than the E-baseline, the LHCEsenabled superior low-temperature discharge performances, as evidenced bythe significantly higher capacity retentions in the full range of thetesting temperatures, better recovery of the capacity when thetemperature was set back to 25° C. and greatly smaller voltage decaythan the conventional LiPF₆ electrolyte, which should be attributed tothe more conductive electrode/electrolyte interfaces formed in theLiFSI-based LHCEs. As for E-baseline, when the operating temperaturedecreased from 25° C. to 0° C., −10° C., −20° C. and −30° C., thedischarge capacity retention compared to that of 25° C. (189 mAh g⁻¹)continually decreased to 92.6%, 83.1%, 37.0% and 1.6%, respectively,accompanied by severe voltage decay (FIG. 19A). The cell usingE-baseline failed at and below −20° C. In comparison, the cell withAE003 showed negligible discharge capacity fading and voltage decay whenthe temperature reduces from 25 to 0° C. and −10° C. (FIG. 19D). Whenoperating at −30° C., the discharge capacities of the cells withAE001-AE003 were 106.5, 154.9, and 160.7 mAh g⁻¹, corresponding tocapacity retentions of 55.6%, 81.1% and 85.6% and energy densityretentions of 47.1%, 72.1% and 76.0%, respectively (compared to 25° C.).When further decreasing the temperature to −40° C., the cells with LHCEsall suffered sharp capacity drop, but the capacity retentions still were30.7%, 29.2% and 46.2%, respectively. The differential scanningcalorimetry (DSC) scan in FIG. 20 confirmed the absence ofsolidification in LHCEs. The peaks at about 2-3° C. are due to themelting of ice formed during cooling process of the samples in liquidnitrogen. Therefore, it is speculated that the accelerated increase ofviscosities when temperatures are lower than −30° C. in LHCEs (FIG. 8B)should contribute to the fast capacity decay at −40° C. When the workingtemperature turns back to 25° C. after the low-temperature dischargingtests, the reversible capacities of the cells with AE002 and AE003 fullyrecovered, with negligible voltage decay (FIGS. 18 and 19C,D); while forthe cells with E-baseline and AE001, 95.5% and 93.4% of the dischargecapacities were recovered, respectively. It is seen from thelow-temperature tests that AE003, which contains a small portion of ECwith high-melting point, presented better low-temperature dischargeperformance than the LHCEs without EC. This is significantly differentfrom the previous reports, in which EC plays an adverse effect on thelow-temperature discharge capacity of LIBs using the LiPF₆/carbonateelectrolyte (Lie et al., ACS Appl. Mater. Interfaces 2017, 9:18826). Itis speculated that the small portion of EC in AE003 is beneficial to theformation of a robust and more conductive electrode/electrolyteinterface layer, resulting in superior Li⁺ ion transfer kinetics whichenables the better low-temperature discharge performance in the cellswith AE003 than in AE001 and AE002.

Overall, the Gr∥NMC811 full cells using LHCEs exhibited significantlysuperior electrochemical performances in terms of long-term cyclingstability at room temperature and high temperature, capacity retention,voltage stability, rate capability and low-temperature dischargingbehavior in comparison with E-baseline cells at a high cutoff voltage of4.4 V. These performances are the best ever reported for LIBs based on ahigh energy density NMC811 cathode and Gr anode at a high charge cutoffvoltage. In addition, the results demonstrated that the electrolyteconductivity and viscosity were not the major controlling factors forthe LIB performances at fast charging/discharging and low-temperaturedischarge. Therefore, Gr∥NMC batteries combining the high energy densityNMC811 cathode, and the highly stable electrolytes of LHCEs, especiallyAE003, are a promising energy storage system for wide-temperature-range(from −30 to 60° C.) applications.

Graphite/Electrolyte Interface

In LIBs, the electrolyte stability on the Gr anode is a significantfactor for the cell performances. The XRD (FIG. 21) and SEM (FIG. 22)were firstly used to characterize the crystalline structures andmorphologies of the Gr anodes, respectively, after 100 cycles at 60° C.in the four electrolytes. The XRD patterns show that the Gr cycled inAE003 took negligible changes away from the pristine one, indicating thesuperior structural integrity of Gr layers after cycling. The SEM imagesof cycled Gr particles in FIGS. 22A-22D showed insignificant differencein the four electrolytes except for the covered surface layers which mayexhibit different thicknesses. Under high resolution transmissionelectron microscope (HRTEM), the pristine Gr showed a clean surface(FIG. 23A). After 100 cycles in E-baseline, a non-uniform surface layerof 3-6 nm thick was covered on the Gr (FIG. 23B), which should bederived from the decomposition of the electrolyte, mainly EC and LiPF₆.When the electrolyte was changed to AE001, the LHCE of 1.4 MLiFSI/DMC-TTE, a slightly thinner SEI of around 3-5 nm was generated onthe Gr anode (FIG. 23C). However, the similar thickness of SEI layersformed in E-baseline and AE001 leads to totally differentelectrochemical performance in wide temperatures, implying the greatdifference in the composition of the SEI layers. Furthermore, with theuse of a small amount of VC to replace equal amount of DMC, a morehomogeneous and thinner SEI was formed on the Gr anode with a thicknessof ca. 1.5 nm in AE002 (FIG. 23C). With further modification byreplacing the VC with the same amount of EC, an even more homogeneousand thinner SEI layer of ca. 1 nm was observed on the Gr anode in AE003(FIG. 23A). As demonstrated by the well-maintained Gr layer structure inthese three LHCEs shown in FIGS. 23C-23E and their stable cyclingperformance in FIGS. 11A-11B, the SEI films formed on the Gr anodes inthese LHCEs are thin but robust. In addition, as evidenced by the EISresults of the Gr∥NMC811 cells before and after 100 cycles at 60° C.shown in FIG. 14 and Table 3, the SEI films formed in these LHCEsespecially AE002 and AE003 are much more ionically conductive. Theseobservations are also consistent with the greatly improved batteryperformances in wide-temperature cycling, rate capability andlow-temperature discharge shown in FIGS. 16A-B and 18.

To analyze the electrolyte decomposition products on the cycled Granodes, XPS was further conducted. The elements and their related atomicratios detected in the SEI layers are summarized FIG. 24. It is seenfrom FIG. 24 that the SEs from the four electrolytes had roughly similarcontents of Li, C and O, but the SEI from E-baseline had much highercontent of F than the ones from the three LHCEs. On the other hand, Pwas only detected in the SEI from E-baseline, while N and S were onlyfound in SEIs for the three LHCEs, which are from the decompositions ofthe salt anions used in the related electrolytes, respectively. Whenanalyzing the narrow scan XPS spectra, it was found that the SEIcomponents from E-baseline were significantly different from those inthe LHCEs because of the involvement of different anions and solvents.The three LHCEs showed similar SEI components but differentcompositions, as suggested by the detailed elemental distributions ofthe SEI on Gr anodes in FIGS. 25, 26. Combining the results from the C1s and O 1s spectra, it can be observed that the SEI formed inE-baseline contained more organic compounds due to the increasedproducts from the solvent reduction/decomposition and supported by thehigher amounts of C—C/C—H, C═O and C—O contained species, as found inthe measured surface layer composition. However, the nature of the SEIsformed in the LHCEs was more inorganic, as a result of significant saltreduction/decomposition products such as Li₂O. This effect along withthe appearance of C (C—SO, 287.7 eV, C 1s), N (N—S, 398.4 eV, N 1s) andS (S—O, 167.3 eV and S—N, 169.2 eV, S 2p) signals and the decrease ofC=0 (531.1 eV, O 1s) signal on the surface films imply that the SEIlayers in LHCEs derived mainly from FSI⁻ anions and could effectivelyinhibit further side reactions of the solvent. The slight amount of C—Fspecies found in the LHCEs indicates the participation of TTE in the SEIformation. Combining with the electrochemical performances in FIGS.11A-11B, the higher contents of F, N and S species in AE003 than thosein AE001 and AE002 (FIG. 24) may suggest the improved SEI passivatingability from more completed FSI⁻ sacrificial decomposition. Therefore,these LiFSI-based LHCEs diluted with TTE created a Li-rich interphase byearly-onset reduction of the salt anion and effectively suppressed thesolvent reduction/decomposition, enabling unprecedented and highlyreversible cycling based on Gr anode in high voltage window and moreoverexhibiting fast ion conduction and stability over a wide temperaturerange. Meanwhile, obviously much higher Ni 2p signal could be seen onthe Gr anode cycled in E-baseline while the Ni 2p signal is hardlydetected on the Gr anodes cycled in the three LHCEs. The Ni is from theNMC cathode. The Ni 2p results indicate the LHCEs can enable a muchbetter protective CEI than E-baseline in such high cut-off voltage,enabling superior cathode stability.

Cathode/Electrolyte Interface

To understand the origin of the excellent cycling stability andremarkably improved wide-temperature performance of the LHCEs over theconventional LiPF₆/carbonate electrolyte in Gr∥NMC811 cells, the cycledNMC811 cathodes and their surface layers (i.e. the cathode/electrolyteinterfaces) after 100 cycles at 60° C. were also characterized by SEM,XRD, HRTEM and XPS. As shown by the SEM images of surface view on NMC811particles in FIGS. 27A-27J and the FIB/SEM images of the cross-sectionview on single NMC811 particles in FIGS. 28A-28E, cracking in secondaryand primary particles as well as the bulk of the cycled NMC811 cathodein E-baseline was obviously observed as indicated by the arrows (FIGS.27C, 27D), which can be attributed to the severe changes in crystallineparameters of NMC811 as indicated in the peak shifts of (003) and(108)/(110) reflections to lower/higher scattering angles, by the XRDpatterns in FIGS. 29A-B, also which may contribute to the rapid capacityfading. On the contrary, the NMC811 particles cycled in the three LHCEswell maintained their integration (FIGS. 27E-27J) and fewer changes incrystalline parameters (FIGS. 29A-B). FIGS. 29A-B show that moresignificant shifts to lower-high scattering angles were observed in theE-baseline electrolyte than in the LHCEs, indicating the more severeelongation/shrinkage of the crystal axis, i.e., more drasticdeformations of the crystal volume, which have been reported to be amain contribution toward particle cracking during cycling. These resultsagree with the SEM images of FIGS. 27A-27J and 28A-28E, in which theprimary and secondary particles of cycled NMC811 using E-baselinepresented obvious cracks, compared to the imperceptible cracks inAE001-AE003. Furthermore, as shown by the TEM image in FIG. 28F, thepristine NMC811 presented a clean surface. While, after 100 cycles inE-baseline, a non-uniform CEI layer with a thickness of 1521 nm wasobserved on the cycled NMC811 (FIG. 28G). When the electrolytes were theLHCEs, the CEI layers on the surfaces of the cycled NMC811 were muchmore uniform and thinner than that in E-baseline, of which thethicknesses were 5 nm for AE001 (FIG. 28H), 4 nm for AE002 (FIG. 28I)and 3 nm for AE003 (FIG. 28J). Although the CEIs in AE001-AE003 weremuch thinner, they were more robust and protective, as demonstrated bythe negligible Ni dissolution in LHCEs compared to that of theE-baseline (FIGS. 24 and 26). These results indicate that manipulatingthe salt/solvent/additive chemistry of the electrolytes enablesefficient protection on the NMC cathode, which further helps inhibitelectrolyte decomposition and transition metal dissolution andcorrespondingly suppress particles cracking.

The elements and their related atomic ratios detected in the CEI layersare summarized in FIG. 30A, and the detailed narrow scan XPS spectra areshown in FIGS. 30B-30C and 31. Similar to SEIs on cycled Gr anodes, theCEIs from the four electrolytes had similar contents of Li, C, O and F,but P was also found in the CEI from E-baseline while N and S weredetected in CEIs for the three LHCEs, which are from the decompositionsof the salt anions and solvents used in the related electrolytes,respectively. When analyzing the narrow scan XPS spectra, it is seenfrom the C 1s spectra in FIGS. 30B and 31 that the CEI components oncycled NMC811 cathodes in the four electrolytes were similar, includingthe conductive carbon (C—C/C—H, 284.8 eV, C 1s), the PVDF binder(CF₂—CH₂, 287.5 eV, C 1s and C—F, 290.7 eV, C 1s), and the M-O species(529.6 eV, O 1s). For the O 1s spectra (FIGS. 30C and 31), significantlyincreased C═O and possible O—H signals were found on the cathodes cycledin AE001-AE003, suggesting DMC molecules are involved in the CEIformation process. In addition, the apparent signals of S-Ox/N—O, (534.0eV, O 1s) indicate the decomposition of salt anion FSI—, which wasfurther confirmed by the N—OX (400.1 eV, N 1s) and S—OX (169.5 eV, S 2p)signals presented in FIG. 31. In the F 1s spectra (FIGS. 30D and 31),the cycled cathode in E-baseline showed a much stronger LiF signal(685.4 eV, F 1s) than those in LHCEs, indicating serious corrosion bythe trace amount of hydrofluoric acid (HF) in the LiPF₆ electrolyte. ThePO_(y)F_(z) ⁻ signals (685.4 eV, F 1s in FIG. 30D and 135.9 eV, P 2p inFIG. 31) also confirmed the decomposition of LiPF₆. The presence oflarge amount of highly resistive LiF on the cathode surface is reportedto be detrimental to Li⁺ transport kinetics, resulting in capacityfading (Zhao et al., Adv. Energy Mater. 2018, 8: 1800297). In addition,the HF has the potential to attack the surface of the layered cathode,which may aggravate Li⁺/Ni²⁺ cation mixing as well as disorderedrock-salt phase formation due to insufficient coordinating oxygencontributed to the corrosion reactions. Hence, the much lower content ofLiF on cathodes cycled in LSEs, as indicated by the weaker Li—F signalsin FIGS. 30D and 31 and lower contents of Li in FIG. 30A, largelycontribute to the significantly improved cycling performance whencompared to E-baseline. On the other hand, more apparent signals of C—Fspecies (FIGS. 30D and 31) were observed on the NMC811 surfaces cycledin LHCEs, especially in AE003, suggesting the fluorinated ether diluent,TTE, participates in the CEI formation on the NMC811 surface. It wasfound that all the LHCEs presented similar C 1s, S—OX/N—OX and M-Osignals, while the difference lies in N 1s, S 2p, C═O/O—H, C—F and Li—F.With the best electrochemical performance, AE003 exhibited the lowestcontent of C═O/O—H and the strongest signal of C—F (also indicated bythe lowest atomic ratio of Li but the highest atomic ratio of F as shownin FIG. 30A), implying the unfavorable role of DMC and the beneficialeffect of TTE in the CEI formation on the NMC811 surface. And the lowestand sub-lowest intensities of N 1s and S 2p signals in AE003 and AE002respectively, combining the performance in cycling and rate capability,imply moderate decomposition of salt anion FSI⁻ enables a more robustand conductive CEI on the NMC811 cathode.

At the same time, obviously much higher Ni 2p signal seen on the Granode cycled in E-baseline compared to those in the LHCEs again provedthe LHCEs can enable a much better protective CEI than E-baseline insuch high cut-off voltage (FIG. 26), enabling superior cathodestability. The characterization results demonstrate that theelectrode/electrolyte interfaces on both anode and cathode are the majordominating factors for the LIB performances.

Example 3 Additional DMC-Based Electrolytes for Cells with GraphiteAnodes Experimental:

Chemicals and materials: LiPF₆, EC, DMC, EMC, VC, DME and acetonitrile(AN) in battery grade were acquired from Gotion and used as received.LiFSI in battery grade was obtained from Nippon Shokubai Co., Ltd. andwas dried at 100° C. overnight before use. TMPa, TEPa, dimethylmethylphosphonate (DMMP) and TMS, were ordered from Sigma-Aldrich. TTEwas purchased from SynQuest Laboratories. Li chips were ordered from MTICorporation. TMPa, TEPa, DMMP, TMS and TTE were used after pre-dryingwith molecular sieves. All electrolytes were prepared inside a glove boxfilled with purified argon, where the moisture and oxygen contents wereless than 1 ppm. The moisture content in the organic solvents andelectrolytes was measured by Karl-Fisher titration to make sure thewater content was less than 20 ppm.

Coin cell assembly and electrochemical tests: CR2032-type coin cellswere used to test the cycling performance of the electrolytes indifferent battery systems. Gr anode (with an areal capacity loading of3.5 mAh cm⁻²) and NMC811 cathode (with an areal capacity loading of 2.8mAh cm⁻²) were used. The coin cells were assembled in the argon-filledglove box by using a piece of cathode disk (1.27 cm⁻²), a piece ofpolyethylene separator, a piece of anode disk (1.77 cm⁻²), and 100 Lelectrolyte. The half cells and full cells were cycled on a Landt testerat 25° C. after three formation cycles.

Two additional electrolytes, AE004 and AE005 were prepared. All fiveelectrolytes are shown in Table 4.

TABLE 4 Electrolyte formulation, density, conductivity and viscosity(all at 25° C.) of the baseline electrolyte and the LHCEs. ElectrolyteDensity Conductivity Viscosity Code Electrolyte formulation (g ml⁻¹) (mScm⁻¹) (cP) E-baseline 1.0M LiPF₆ in 1.39 6.07 3.35 EC-EMC (3:7 by wt.) +2 wt. % VC AE001 1.4M LiFSI in 1.50 1.40 3.67 DMC-TTE (2.2:3 by mol.)AE002 1.4M LiFSI in 1.55 1.05 3.53 DMC-VC-TTE (2:0.2:3 by mol.) AE0031.4M LiFSI in 1.49 1.07 3.69 DMC-EC-TTE (2:0.2:3 by mol.) AE004 1.4MLiFSI in 1.49 0.76 4.08 DMC-EC-TTE (1.6:0.6:3 by mol.) AE005 1.4M LiFSIin 1.48 0.69 5.88 DMC-EC-VC-TTE (1.4:0.6:0.2:3 by mol.)

The electrochemical stabilities of the six electrolytes on Gr anode andat high voltages were first evaluated by CV in Li∥Gr cells and LSV inLi|Li|SP-PVDF/Al three-electrode cells, respectively. It is seen fromthe CV curves in FIG. 32A that all five LHCEs showed good stability onGr anode as the baseline electrolyte did, enabling the evaluation ofthese new electrolytes in Gr-based LIBs. The lower response currentdensities for the LHCEs than that for E-baseline were possibly due tothe lower room-temperature ionic conductivities of LHCEs (Table 4). Onthe high voltage side, the LSV scans in FIG. 32B show theelectrochemical anodic decomposition (with a response current density of0.05 pA cm⁻²) on SP-PVDF/AI electrode started at 4.70 V in AE001, 4.60 Vin AE002, 4.93 V in AE003, 4.83 V in AE004, 4.58 V in AE005 and 4.74 Vin E-baseline. Although AE001, AE002 and AE005 showed slightly loweroxidation potentials than E-baseline, the former three electrolytesexhibited much lower current density after 4.96 V than the controlelectrolyte, indicating the good passivation formed from the threeLHCEs. Overall, AE003 exhibited superior oxidative stability and goodcompatibility with Gr electrode, being expected to give advancedelectrochemical performances.

The long-term cycling stability, rate capability and low-temperaturedischarge performance of the five LHCEs and the E-baseline wereinvestigated in Gr∥NMC811 coin cells under the voltages range of 2.5-4.4V after three formation cycles performed at C/20 for the first cycle andC/10 for the other two cycles, where 1C corresponds to 2.8 mA cm⁻². Thevoltage profiles of the first formation cycle of the cells withdifferent electrolytes at 25° C. are shown in FIG. 33A. The cells withthe six different electrolytes showed slightly different curves duringcharge, possibly because of the different oxidations of the electrolytecomponents, but their discharge curves were nearly the same. The cellsusing AE003 and AE004 showed the highest discharge capacity of 194.3 and195.3 mAh g⁻¹ and also the highest Coulombic efficiency (CE) of 80.8%and 81.5%, respectively, at the first cycle, while the cells using otherfour electrolytes (AE001, AE002, AE005 and E-baseline) exhibited similardischarge capacities of 188.4, 186.8, 183.9 and 188.5 mAh g⁻¹,respectively and the CE values were 78.8% for AE001, 79.3% for AE002,78.8% for AE005 and 77.9% for E-baseline.

FIG. 33B shows the long-term cycling stability of Gr∥NMC811 coin cellswith the six electrolytes at 25° C. under the charge/discharge rate ofC/3 after three formation cycles, and the corresponding cycling CEs andthe voltage profiles at selected cycles are shown in FIGS. 34A-34G. Itis clearly observed that although the cell with E-baseline electrolyteexhibited slightly higher discharge capacities than the five LSEs in thefirst 100 cycles, it has an abrupt capacity drop after that (FIG. 33B),with capacity retentions of 71.5% and 12.5% at the 150^(th) and 200^(th)cycles, respectively (compared to the capacity of the first cycle at C/3rate after the three formation cycles), and a fluctuation of cycling CEsafter 150 cycles (FIG. 34A). This can be attributed to the poorelectrode/electrolyte stability of E-baseline on both Gr and NMC811 andthe aggressive side reactions of E-baseline with the Ni-rich NMCmaterial, especially the highly reactive Ni⁴⁺, which will be discussedlater. The consequence is the quick accumulation of resistive surfacefilms on Gr and NMC811 surfaces and accordingly the increasedoverpotential (FIG. 23B), leading to the battery failure at an earlystage.

In comparison, the cells with all five LHCEs exhibited significantlyimproved cycling stability. The cells with AE001 and AE002 gavedischarge capacities of 179.8 and 172.9 mAh g⁻¹ at the 400^(th) cyclewith capacity retentions of 100% and 98.6%, respectively. After that,the cell with AE001 experienced capacity fading accompanying with CEfluctuation and voltage polarization, which are more severe after the500^(th) cycle (FIGS. 34A, 34C), resulting in a capacity retention of40.7% after 600 cycles. When part of DMC in AE001 was replaced with VC(i.e. AE002), no capacity attenuation and slight overpotential increasewere observed in the cell with AE002 during the 600 cycles (FIGS. 33Aand 34D), but the capacity and the CE exhibited fluctuations, anirregular behavior after 400 cycles (FIGS. 33B and 34A), indicating theoccurrence of side reactions in the cell with AE002 after long-termcycling. When the VC in AE002 was replaced by equal EC, significantimprovement in cycling stability in terms of capacity, CE andoverpotential were obtained in the cell with AE003 (FIGS. 33A, 34A,34E). The discharge capacity at the 600^(th) cycle for the cell withAE003 was 173.4 mAh g⁻¹, corresponding to a capacity retention of 94.2%.Meanwhile, the CE stayed at 99.9% during the 600 cycles for the cellwith AE003, much more stable than the CEs for the cells with AE001 andAE002 (FIG. 34A). This is probably because the participation of ECbenefits the formation of uniform and robust SEI on Gr and CEI onNMC811. More importantly, there was negligible increase in celloverpotential during 600 cycles for the cell with AE003 (FIG. 34E),indicating that the electrode/electrolyte interphase layers were highlyconductive for Li⁺ ion transportation under the participation of EC. Thefavorable role of EC was further confirmed by the stable cycling (FIG.33A) and negligibly increased overpotential (FIG. 34F) during 600 cyclesfor the cell using AE004 (in which the content of EC was higher thanAE003). While for the cell using AE005, the reversible capacity slightlyincreased with the cycling (FIG. 33B) and after 600 cycles there was anobvious growth of overpotential.

In the conventional LiPF₆/carbonate electrolyte, an increase in testingtemperature will drastically accelerate the parasitic reactions ofelectrolyte on both high-Ni NMC cathode and Gr anode. This willaccelerate the degeneration of NMC cathode and cause the formation ofmore resistive components in the SEI film of Gr anode, which in turnresults in fast capacity loss. The cycling performance of the Gr∥NMC811coin cells was evaluated with the six electrolytes under 60° C. afterthree formation cycles at 25° C. As seen from FIG. 33C, the cell withE-baseline exhibited a sharp capacity drop at the 35^(th) cycle and thecapacity retention after 50 cycles was only 19.4%, accompanying withobviously increased voltage polarization (FIG. 35C). In contrast, thecells with AE001-AE005 demonstrate superior high-temperature cyclingperformance with the reversible capacities of 174.3, 177.9, 183.6, 176.0and 175.2 mAh g⁻¹ after 100 cycles (FIG. 33C), corresponding to capacityretentions of 90.2%, 91.8%, 94.9, 94.8 and 92.8%, respectively, withlimited increase in overpotential during the 100 cycles (FIGS. 35A-35G).

The rate capabilities of the five LSEs and the E-baseline at different Crates were also evaluated in Gr∥NMC811 cells by two testing protocols.Under the protocol with a constant charge rate of C/5 and differentdischarge rates from C/5 to 5C, as shown in FIG. 33D, the cell withAE003 showed the superior discharge rate capability in the full raterange while the baseline electrolyte suffered rapid capacity fading whendischarge rates were 3C and 5C. The cell with AE005 presented worsedischarge rate capability than all the other LHCEs in the full range ofrate. The cells with AE001 AE002 and AE003 exhibited similar dischargerate capability like E-baseline at 1C rate and below but betterperformance than E-baseline at discharge rates of 3C and 5C. When thedischarge rate was changed back to C/5, the cells with all sixelectrolytes had similar discharge capacities. As for the protocol withdifferent charge rates from C/5 to 5C but the same discharge rate of C/5(FIG. 33E), the cells with AE002 and AE005 showed inferior ratecapability than the cells with other LHCEs and the baseline electrolytefrom C/5 to 5C. The cell with AE001 had similar reversible capacities tothe cell with E-baseline when the charge rate was up to 2C, the cellwith AE003 maintained the same rate capability as the cell withE-baseline till 3C rate during charging, and the cell with AE004 showedslightly better rate capability than E-baseline from C/5 to 3C andsimilar capacities with that of E-baseline at 5C. When the charge ratewas increased to 5C, the cells with all LHCEs except AE004 showed verylimited capacity, lower than the cell with E-baseline. However, when thecharge rate was set back to C/5, the recovering discharge capacity fromhigh to low followed the order ofAE004>>AE003>>AE005>>AE002>AE001>>E-baseline. The results from both ratecapability testing protocols demonstrated the superior rate performanceof the cells with AE003 up to 3C rate, indicating the more conductiveelectrode/electrolyte interfaces on both Gr and NMC811 electrodes andcorrespondingly fast electrode redox reaction kinetics in the cells withAE003.

Furthermore, the low-temperature discharging performance of the LHCEsand E-baseline was performed (25° C. to −40° C.), as shown in FIG. 33F.Even with much lower ionic conductivities and doubled viscosities underlow temperatures than the E-baseline (FIGS. 36A-36B), the LHCEs enabledsuperior low-temperature discharge performances, as evidenced by thesignificantly higher capacity retentions in the full range of thetesting temperatures, better recovery of the capacity when thetemperature is set back to 25° C. and greatly smaller voltage decay thanthe conventional LiPF₆ electrolyte (FIGS. 37A-37F), which should becontributed to the more conductive electrode/electrolyte interfacesformed in the LiFSI-based LHCEs. As for E-baseline, when the operatingtemperature decreased from 25° C. to 0° C., −10° C., −20° C. and −30°C., the discharge capacity retention compared to that of 25° C. (189 mAhg⁻¹) continually decreased to 92.6%, 83.1%, 37.0% and 1.6%,respectively, accompanying with severe voltage decay (FIG. 37A).Obviously, the cell failed at and below −20° C. In comparison, the cellwith AE003 showed negligible discharge capacity fading and voltage decaywhen the temperature reduced from 25 to 0° C. and −10° C. (FIG. 37D).When operating at −30° C., the discharge capacities of the cells withAE001-AE005 were 106.5, 154.9, 160.7, 157.6 and 146.3 mAh g⁻¹,corresponding to capacity retentions of 55.6%, 81.1%, 85.6%, 83.4% and81.3% and energy density retentions of 47.1%, 72.1%, 76%, 73.4 and69.8%, respectively (compared to 25° C.). When further decreasing thetemperature to −40° C., the cells with LHCEs all suffered sharp capacitydrops, but the capacity retentions still were 30.7%, 29.2%, 46.2%, 44.0%and 32.2%, respectively. It is speculated that the accelerated increaseof viscosities when temperature is lower than −30° C. in LHCEs (FIG.36B) should contribute to the fast capacity decay at −40° C. When theworking temperature turns back to 25° C. after the low-temperaturedischarging tests, the reversible capacities of the cells withAE002-AE005 were completely recovered, with negligible voltage decay(FIGS. 33F and 37C, 37D); while for the cells with E-baseline and AE001,95.5% and 93.4% of the discharge capacities were recovered,respectively. It is seen from the low-temperature tests that AE003,which contains a small portion of EC with high-melting point, presentedbetter low-temperature discharge performance than the LHCEs without ECand the one with more EC (AE004). This is significantly different fromthe previous reports, in which EC played an adverse effect on thelow-temperature discharge capacity of LIBs using the LiPF₆/carbonateelectrolyte. It is speculated that the small portion of EC in AE003 isbeneficial to the formation of a robust and more conductiveelectrode/electrolyte interface layer, resulting in superior Li⁺ ionstransfer kinetic which enables the better low-temperature dischargeperformance in the cells with AE003 than in the other LHCEs.

Example 4 Electrolytes with Varying Solvents for Cells with Graphite,Silicon/Carbon Composite, or Silicon Anodes Experimental:

Chemicals and materials: LiPF₆, EC, DMC, EMC, VC, FEC, DME and AN inbattery grade were acquired from Gotion and used as received. LiFSI inbattery grade was obtained from Nippon Shokubai Co., Ltd. and was driedat 100° C. overnight before use. TMP_(a), TEP_(a), DMMP and TMS werepurchased from Sigma-Aldrich. TTE and TFEO were purchased from SynQuestLaboratories. Li chips were ordered from MTI Corporation. TMP_(a),TEP_(a), DMMP, TMS, TTE and TFEO were used after pre-drying withmolecular sieves. All electrolytes were prepared inside a glove boxfilled with purified argon, where the moisture and oxygen contents wereless than 1 ppm. The moisture content in the organic solvents andelectrolytes was measured by Karl-Fisher titration to make sure thewater content was less than 20 ppm.

Coin cell assembly and electrochemical tests: CR2032-type coin cells(ordered from MTI Corporation) were used to test the cycling performanceof the electrolytes in different battery systems. Graphite (Gr) orsilicon/carbon (Si/C) composite or Si anodes andLiNi_(0.6)Mn_(0.2)Co_(0.2)O₂ (NMC622) or LiNi_(0.8)Mn_(0.1)Co_(0.1)O₂(NMC811) or LiNi_(0.96)Mg_(0.02)Ti_(0.02)O₂ (NMT) cathodes were used.The coin cells were assembled in the argon-filled glove box by using apiece of cathode disk (1.27 cm⁻²), a piece of polyethylene (PE)separator, a piece of anode disk (1.77 cm⁻²), and certain amount ofelectrolyte. To avoid corrosion to the stainless-steel positive cans bythe electrolyte at high voltages, the Al-clad positive cans were used toassemble the full cells. An extra piece of Al foil (2.83 cm⁻²) was alsoadded in between the cathode disk and the Al-clad positive can. The fullcells were cycled on a Landt tester or an Arbin tester at 25° C. orother selected temperatures after three formation cycles at 25° C.

In addition to the electrolytes of Example 3, LHCEs based on othersolvents were also systematically studied. The electrolyte formulae aresummarized in Table 5.

TABLE 5 Electrolyte formulae Code Electrolyte formulation E257 1.0MLiPF₆/EC-EMC (3:7 wt.) E268 1.0M LiPF₆/EC-EMC (3:7 wt.) + 2 wt. % VCE001 LiFSI:DMC:TTE = 1.0:2.2:3.0 by mol. E002 LiFSI:DME:TTE =1.0:1.1:3.0 by mol. E003 LiFSI:TMP_(a):TTE = 1.0:1.4:3.0 by mol. E004LiFSI:DMMP:TTE = 1.0:1.4:3.0 by mol. E005 LiFSI:AN:TTE = 1.0:3.3:3.0 bymol. E009 LiFSI:TMS:TTE = 1.0:3.0:3.0 by mol. E010 LiFSI:TEP_(a):TTE =1.0:1.4:3.0 by mol.

A piece of PE separator, Gr electrode disk (from Argonne NationalLaboratory, 1.77 cm⁻²), and NCM811 electrode (from Argonne NationalLaboratory, 1.27 cm⁻²), were assembled into CR2032-type coin cells with50 μL electrolyte. The cells were conducted three formation cycles (C/20for 1 cycle and C/10 for 2 cycles) and then regularly cycled at C/3charging and 1C discharging in the voltage range of 2.5-4.4 V.

FIG. 38 shows the cycling performance of Gr∥NCM811 full cells usingLHCEs with different solvents without VC additive. The cells withphosphorus-containing solvents, including TMP_(a), TEP_(a) and DMMP, allshowed sudden capacity decays after being charged and discharged for acertain number of cycles. The reason can be probably assigned to thefailure of SEI and/or CEI. Only TMS-based cells showed excellentcapacity retention. The results indicated that without VC additive, fewLHCEs show superior cycling performance in Gr∥NMC811 cells.

DME-based electrolytes: In response to this challenge, additives wereintroduced into the LHCEs. A series of DME-based LHCEs were prepared asshown in Table 6.

TABLE 6 Electrolyte formulae Code Electrolyte formula E268 1.0MLiPF₆/EC-EMC (3:7 wt.) + 2 wt. % VC E002 LiFSI:DME:TTE = 1.0:1.1:3.0 bymol. E002V LiFSI:DME:TTE:VC = 1.0:1.1:3.0:0.2 by mol. E002ELiFSI:DME:TTE:EC = 1.0:1.1:3.0:0.2 by mol. E002F LiFSI:DME:TTE:FEC =1.0:1.1:3.0:0.2 by mol.

Dependence of viscosities and ionic conductivities of E268 and DME-basedLHCEs on temperature was evaluated. As shown in FIG. 39A, the DME-basedLHCEs exhibited a higher viscosity than the E268 in the measuredtemperature range. At room temperature (25° C.), the viscosities ofE268, E002, E002V, E002E and E002F were determined as 2.78, 5.15, 4.96,5,18, 5.10 mPa s. As a result of higher viscosity and low amount ofdissociation solvent, DME-based LHCEs exhibited lower ionicconductivities than E268 (FIG. 39B). At the room temperature, the ionicconductivities of E268, E002, E002V, E002E, E003F are determined as8.94, 1.90, 1.90, 2.36, 2.31 mS cm⁻¹, respectively.

FIG. 40A shows the charge/discharge voltage-specific capacity profilesat the first formation cycle at C/20 rate for Gr∥NMC811 cells comprisingthe electrolytes listed in Table 6. The cell with E268 had first cyclecharge and discharge capacities of 234.7 and 194.2 mAh g⁻¹, leading to aCE of 82.7%. The cell with E002 had only 236.2 and 149.5 mAh g⁻¹ for thefirst cycle charge and discharge capacities, yielding the first cycle CEof mere 63.3% (FIG. 40B). With the addition of additive VC, EC or FEC inE-DME, the first cycle discharge capacity and CE of the cells wasimproved, 167.9 mAh g⁻¹ and 71.24% for E002V, 175.6 mAh g⁻¹ and 78.1%for E002E, and 191.8 mAh g⁻¹ and 79.0% for E002F. Such improvement ismainly attributed to the good passivation on Gr electrodes by theadditives VC, EC and FEC due to their capability of forming high qualitySEI during the reduction process. As shown in FIG. 40B, at the thirdformation cycle, the three DME-LHCEs already yield the CE close to(98.4% for E002, 97.8% for E002V and 98.5% for E002F) or even over(99.2% for E002E) that of E268 (98.9%).

Upon cycling, the cells comprising E268 and E002F showed normalmonotonous capacity decay, whereas the discharge capacities of the cellscomprising E002 and E002E showed a certain degree of capacity increasedin certain cycling segments (FIG. 41A). The reasons for such an increasein capacity with cycling reasons are not entirely clear. Apparently,electrolyte additives play a highly influential role over the cyclingperformance of cells using DME-based LHCEs. After 500 charge/dischargecycles in the voltage range of 2.5-4.4 V, the capacity retentions of thecells comprising E268, E002, E002E and E002F amounted to 75.8%, 98.5%,95.6% and 86.8%, respectively. It can be inferred that the DME-basedLHCEs are superior electrolytes to state-of-the-artLiPF₆-organocarbonate based electrolyte (E268) in terms of improving thecycle life of high energy LIBs. As indicated in FIG. 41A, the capacityof E002E based cells exhibited a more rapid capacity fading than E002Fcells after approximately 350 charge/discharge cycles. The capacityretentions of E002E and E002F cells from 350^(th) cycle to 500^(th)cycle were determined as 92.7% and 97.3%, respectively. The Coulombicefficiencies were similar and ranged from 99.5-100% (FIG. 41B).

The discharge C-rate performance of the Gr∥NMC811 cells comprising theelectrolytes listed in Table 6 were also evaluated. As illustrated inFIG. 42, due to the significant irretrievable capacity loss in theformation cycles, the E002 cells exhibited relatively low specificcapacities under all selected discharge C-rates. E002V cells exhibitedslightly lower C-rate performance than the E268 due to the relativelylarge capacity loss in the formation cycles. E002E cells showed higherdischarge capacities than E268 cells at all selected C-rates. E002Fresulted in slightly better C-rate performance than E268 under thedischarge C-rates up to 3C, however E-DME-F exhibited lower capacity at5C discharge rate. The reason behind the electrochemical performanceimprovements by DME based electrolytes will be discussed in Example 5later.

The applicability of the E002F (DME-based LHCE with FEC additive) toLIBs with this Co-free LiNi_(0.96)Mg_(0.02)Ti_(0.02)O₂ (NMT) cathode inGr∥NMT cells was also studied. Ultrahigh-nickel layered oxide NMTcathode powder was synthesized and then prepared into a cathode. Granode was from Argonne National Laboratory. E268 was selected as thebaseline electrolyte for comparison. The obtained Gr∥NMT cells wereconducted three formation cycles (C/20 for 1 cycle and C/10 for 2cycles) and then cycled at C/3 charging/discharging in the voltage rangeof 2.5-4.4 V, 1C corresponds to 1.5 mA cm⁻².

As shown in FIG. 43, Gr∥NMT cells using E002F achieved superior capacityretention to those using E268. At 500^(th) cycles, the capacityretentions of Gr∥NMT cells using E268 and E002F amounted to 61.1% and95.3%, respectively. The results demonstrated that the LHCEs screenedfrom Gr∥NMC811 cell chemistry were also qualified to be used in Gr∥NMTchemistry, as extraordinary cycling performance was achieved with E002Fin Gr∥NMT cells.

DMC-based electrolytes: Table 7 shows the compositions of a baselineelectrolyte and a DMC-based LHCE.

TABLE 7 Electrolyte formulae Code Electrolyte formula Baseline 1.0MLiPF₆/EC-EMC (3:7 wt.) + 2 wt. % VC AE012 LiFSI:DMC:TTE:FEC =1.0:2.0:3.0:0.2 by mol.

Gr∥NMT coin cells with AE012 and Baseline electrolyte were assembled inan argon-filled glove box, conducted three formation cycles (C/20 for 1cycle and C/10 for 2 cycles) and then cycled at C/3 charging/dischargingin the voltage range of 2.5-4.4 V, 1C corresponds to 1.5 mA cm⁻².

FIG. 44 shows the cycling performance of Gr∥NMT cells using AE012 andBaseline, respectively. The cell with AE012 showed lower capacities atthe formation cycles and the initial several cycles at C/3 than the cellusing Baseline. However, after formation cycles, the cell with Baselinesuffered from continuous capacity decay and results in a capacityretention of 80.8% after 200 cycles. In contrast, AE012 enables the cella gradual capacity growth in the first 50 cycles which probably due tothe high viscosity and special solvation structure of the LHCE and thennegligible capacity fade in the following cycles, leading to a highcapacity retention of 99.7% after 200 cycles. It is indicated that theAE012 may be in favor of forming much protective electrode/electrolyteinterphases on both Gr and NMT surfaces when compared to the Baselineelectrolyte, thus enabling much improved cycling stability.

TMPa-based electrolytes with reduced flammability: The compositions ofthe LHCEs can be tuned to achieve different functions. In this example,a flame retardant, TMP_(a), was employed as the solvating solvent forthe preparation of LHCEs to reduce the flammability of the electrolytes.The formulae of the TMP_(a)-based electrolytes are summarized in Table8.

TABLE 8 Electrolyte formulae Code Electrolyte formula E268 1.0MLiPF₆/EC-EMC (3:7 wt.) + 2 wt. % VC E003 LiFSI:TMP_(a):TTE = 1.0:1.4:3.0by mol. E003V LiFSI:TMP_(a):TTE:VC = 1.0:1.2:3.0:0.2 by mol. E003ELiFSI:TMP_(a):TTE:EC = 1.0:1.2:3.0:0.2 by mol. E003FLiFSI:TMP_(a):TTE:FEC = 1.0:1.2:3.0:0.2 by mol.

Similar to DME-based electrolytes, the TMP_(a)-based LHCEs exhibited ahigher viscosity than the E268 in the measured temperature range, asshown in FIG. 45A. At room temperature (25° C.), the viscosities ofE268, E003, E003V, E003E and E003F were determined as 2.78, 7.74, 8.04,8.36, 8.21 mPa s. Due to the higher viscosity of TMP_(a) than DME, E003electrolytes exhibited significantly higher viscosities than DME-basedLHCEs. As shown in FIG. 45B, the ionic conductivities of TMP_(a)-basedelectrolytes were significantly lower. At room temperature, theconductivities of E268, E003, E003V, E003E and E003F were determined as8.94, 0.81, 0.83, 0.82, 0.80 mS cm⁻¹, respectively. Comparing all theTMP_(a)-based LHCEs, it can be inferred that the addition of the smallamount of electrolyte additive did not induce significant viscosity andconductivity change.

The anodic stabilities of E268 and the TMP_(a)-based electrolytes werestudied using a Li∥LiMn204 cell set-up. The anodic stability voltages ofE268, E003, E003V, E003E and E003F were determined to be 4.7 V, 4.9 V,4.6 V, 4.9 V and 4.9 V, respectively, as shown in FIG. 46. Due to theunique solvation structure of LHCEs and the chemical stability ofTMP_(a), TMP_(a)-based LHCEs exhibited higher anodic stability thanE268, with the only exception of E003V. The decomposition of VC in E003Vat 4.6 V was the major reason behind its inferior anodic stability. Thesuperior anodic stabilities of TMP_(a) based LHCEs make them favorablecandidates for high voltage LIB applications.

The C-rate performance and the long-term cycling performance of theGr∥NMC811 cells comprising TMP_(a)-based LHCEs were evaluated. E268 wasselected as the reference electrolyte. As shown in FIG. 47A, cells usingTMP_(a)-based LHCEs generally exhibited relatively inferior C-ratecapabilities than the cells using E268 baseline electrolyte when theC-rate was higher than 2C, which can be attributed to the relatively lowionic conductivities of these electrolytes. As shown in FIG. 47B, theintroduction of the electrolyte additives plays an influential role indetermining the lifespan of the Gr∥NMC811 cells using TMP_(a)-basedLHCEs. Gr∥NMC811 cells using E003 (additive free) exhibited rapidcapacity fading at about the 250^(th) cycle. After the introduction ofEC (E003E), the initial average specific capacity of Gr∥NMC811 cells wasincreased. However, the rapid capacity decay started at an even earlierstage (about the 150^(th) cycle). In comparison, the introduction of VCand FEC into TMP_(a)-based LHCEs effectively extended the cycle life ofGr∥NMC811 cells. After 500 charge/discharge cycles, Gr∥NMC811 cellsusing E003V exhibited an average specific discharge capacity verysimilar to that of Gr∥NMC811 cells using E268. E003F achieved the bestcapacity retention among all the electrolytes listed in Table 8.

TMS-based electrolytes: Several TMS-based LHCEs were prepared as shownin Table 9.

TABLE 9 Electrolyte formulae Code Electrolyte formula E268 1.0MLiPF₆/EC-EMC (3:7 wt.) + 2 wt. % VC E009 LiFSI:TMS:TTE = 1.0:3.0:3.0 bymol. E009V LiFSI:TMS:TTE:VC = 1.0:2.8:3.0:0.2 by mol. E009ELiFSI:TMS:TTE:EC = 1.0:2.8:3.0:0.2 by mol. E009F LiFSI:TMS:TTE:FEC =1.0:2.8:3.0:0.2 by mol.

As illustrated in FIG. 48, TMS-based LHCE (E009) can achieve superiorcycling performance in Gr∥NMC811 cells, even in the absence ofelectrolyte additives. The possible reason can be attributed to theeffective SEI formation ability of TMS. The synergetic effects betweenE009 and electrolyte additives were studied in this example. As shown inFIG. 47, the introduction of EC into E009 improved the initial specificdischarge capacity of the Gr∥NMC811 cells, which was in good agreementwith the results obtained with DME-based and TMP_(a)-based LHCEs. Theintroduction of VC (E009V) led to the capacity increase in the first fewtens of charge/discharge cycles. Although cells using E009F (with FECadditive) exhibited slightly lower initial capacity than the cells usingE268, the capacity decay rate was lower. After 500 charge/dischargecycles, the capacity retentions of E268, E009, E009V, E009E andE009F-based cells were determined to be 75.8%, 81.1%, 88.1%, 66.7%,86.4%, respectively. It should be noted that E009V based cells exhibiteda rapid capacity increase in the first 100 charge/discharge cycles,which contributed to their exceptionally high capacity retention. E009Fwas probably the best electrolyte formula since the E009F cells showedthe lowest decay rate among all the cells illustrated in FIG. 48.

DMC-based LSEs for Si/C-based LIBs: Two DMC-based LHCEs were prepared asshown in Table 10.

TABLE 10 Electrolyte formulae investigated in this example CodeElectrolyte formula Control 90 wt. % [1.0M LiPF₆/EC-EMC (3:7 wt.)] + 10wt. % FEC AE003 LiFSI:DMC:TTE:EC = 1.0:2.0:3.0:0.2 by mol. AE011LiFSI:DMC:TTE:EC:FEC = 1.0:1.7:3.0:0.2:0.3 by mol.

Si/C and NCM811 electrodes were used to assemble Si/C∥NMC811CR2032-typecoin cells with 75 μL electrolyte. The cells were conducted threeformation cycles at C/20 for the first cycle and C/10 for the other twocycles before all the other electrochemical tests in the voltage rangeof 2.8-4.4 V, where 1C corresponds to 5.0 mA cm⁻².

The long-term cycling stability at both room temperature (25° C.) andelevated temperature (45° C.) and the discharge rate capability of thetwo LHCEs (AE003 and AE011) and the control electrolyte wereinvestigated in Si/C∥NMC811 coin cells. FIG. 49A shows that the cellswith AE003, AE011 and the control delivered similar charge and dischargecapacities at both the first formation cycle and the first C/3 cycle at25° C. After long-term cycling at C/3 under both 25° C. and 45° C., theretained capacities in cells with AE011 were much higher than those incontrol. AE003 behaved very similar to AE011 at both temperatures. FromFIG. 49B, it can be observed that the areal capacity of cell using AE011was 2.8 mAh cm⁻² after 200 cycles, corresponding to a capacity retentionof 90.3%, being much higher than the capacity retention of 76.7% (i.e. areversible capacity of 2.3 mAh cm⁻²) in the cell with the controlelectrolyte after 200 cycles at 25° C. AE003 also enabled a capacityretention of 86.8% after 200 cycles, higher than control but slightlylower than AE011. When the operating temperature was elevated to 45° C.,AE011 still enables significantly improved cycling stability asindicated in FIG. 49C. The cell with AE011 exhibited a dischargecapacity of 2.5 mAh cm⁻² at the 200th cycle with a capacity retention of80.6%. AE003 also enabled a capacity retention of 82.6% after 100 cyclesat high temperature. In contrast, just 26.7% (0.78 mAh cm⁻²) of thereversible capacity was maintained after 200 cycles under 45° C. in thecell with control. It is suggested that the functional LHCEs, especiallyAE011, can greatly enhance the cycling stability of Si/C∥NMC811 cellsunder both room and elevated temperatures. Further, the discharge ratecapability of AE003 and AE011 was also evaluated with the comparationwith the control electrolyte after three formation cycles. Under theprotocol with a constant charge rate of C/10 and different dischargerates from C/10 to 1C, as shown in FIG. 49D, the cell with AE011 showeda superior discharge rate capability even compared to the cell usingAE003 in the full rate range, while the control electrolyte sufferedrapid capacity fading when discharge rate was 1C. When the dischargerate was changed back to C/10, AE011 enabled total capacity recovery,while the cells with AE003 and Control both recovered about 90.6% of thereversible capacities, compared to the initial capacities at initialC/10, which indicates the formation of more conductiveelectrode/electrolyte interphases on both Si/C and NMC811 electrodes andconsequently, faster electrode redox reaction kinetics in the cells withAE011.

Carbonate-based LHCEs for Si-based LBs: Beyond the application ofDMC-based LHCEs in Gr- and Si/C-based LIBs, advanced electrolytes withsuitable additives also provided excellent performance in high voltagebatteries with a high Si content anode. The formulations of the LHCEs(AE003, AE011, AE012 and AE013) and the conventional LiPF₆/carbonateelectrolyte for Si based batteries (noted as Si-baseline) studied arelisted in Table 11.

TABLE 11 Electrolyte formulae Electrolyte Code Electrolyte formulaSi-baseline 1.2M LiPF₆ in PC-EMC (3:7 by wt.) + 1 wt. % VC + 7% wt. %FEC AE003 1.4M LiFSI in DMC-EC-TTE (2:0.2:3 by mol.) AE011 1.4M LiFSI inDMC-EC-FEC-TTE (1.7:0.2:0.3:3 by mol.) AE012 1.4M LiFSI in DMC-FEC-TTE(2:0.2:3 by mol.) AE013 1.4M LiFSI in DMC-EC-FEC-TTE (2:0.1:0.1:3 bymol.)

The long-term cycling of these LHCEs and the Si-baseline wasinvestigated in Si∥NMC622 coin cells under the voltages range of2.0-4.35 V with a charge rate of 0.7C and a discharge rate of C/2 aftertwo formation cycles performed at C/10 for the first cycle and C/5 forthe second cycle, where 1C corresponds to a current density of 3 mAcm⁻². The Si anode was pre-lithiated with 30% capacity. FIG. 50 showsthe specific capacity over the long-term cycling using differentelectrolytes, and the corresponding cycling CEs and the voltage profilesat selected cycles are shown in FIGS. 51 and 52. For the Si-baseline,the cell is stable for around 350 cycles and starts a fast decay after350 cycles, with capacity retentions of 82.6% and 38.9% at the 350th and550th cycles, respectively (compared to the capacity of the first cycleat C/3 rate after the two formation cycles). This can be attributed tothe poor electrode/electrolyte stability of Si-baseline electrolyte onboth Si and NMC622, which leads to a quick accumulation of resistivesurface films on Si and NMC622. In comparison, it is clearly observedthat the three LHCEs (AE003, AE012 and AE013) have much higher capacityretentions in Si∥NMC622 cells than the Si-baseline electrolyte. Thecells with AE003, AE012 and AE013 give discharge capacities of 154.9,144.5 and 149.4 mAh g⁻¹ at the 500^(th) cycle with capacity retentionsof 83.7%, 78.1% and 80.8%, respectively.

FIG. 51 shows the corresponding CEs during the long-term cycling asshown in FIG. 50. All the cells with AE003, AE012 and AE013 showed highaverage CE above 99.8% during the cycling, and the detailed values aresummarized in Table 12. One interesting phenomenon was the CEfluctuation during the C rate change at every 50 cycles, where C/5charge/discharge was used for capacity check. Much higher CE fluctuationof 60% after long term cycling was observed in Si∥NMC622 cells withSi-baseline and AE011 electrolytes, where the fluctuation significantlyescalated after 350 cycles, which is in consistent with the fastcapacity decay after 350 cycles in these two electrolytes. ElectrolytesAE003, AE012 and AE013 had much smaller CE fluctuation within 10% after500 cycles. For CE fluctuation beyond 500 cycles, the AE012 was thesmallest, constant with the stable cycling as shown in FIG. 50. Theseresults demonstrated that the cells using optimized LHCEs have muchlower resistance and better kinetics after long term cycling, which canbe attributed to the significantly improved SEI and CEI properties on Sianode and NMC622 cathode cycled in such LHCEs.

TABLE 12 First cycle Coulombic efficiency (FCE) and average Coulombicefficiency (ACE) during cycling of the Si-baseline electrolyte and thefour LHCEs studied in this Example. 25° C. (Si with 30% pre-lithiation)45° C. (Si without pre-lithiation) Electrolyte FCE/% ACE/% FCE/% ACE/%Si-baseline 91.05 99.84 84.88 99.6 AE003 90.94 99.88 84.57 99.81 AE01186.84 99.72 83.59 99.8 AE012 88.87 99.89 84.99 99.84 AE013 91.02 99.8185.03 99.81

The voltage profiles of selected cycles during cycling are given inFIGS. 52A-52B, where AE003 represents the optimized LHCE and Si-baselinewas compared as a reference. For the cell using Si-baseline, theoverpotential increased significantly upon cycling with a 0.6 V changefrom the 3^(rd) cycle (first cycle after 2 formation cycles) to 500thcycle, evidence of the large resistance increases during cycling.However, for the cell using AE003 electrolyte, the overpotential atinitial charge state barely changed during long-term cycling, suggestinga much smaller change of resistance.

In addition, Si∥NMC622 cells were also tested at elevated temperature of45° C. To simplify the testing and approximate practical conditions, theSi anode was not pre-lithiated in the Si∥NMC622 cells tested at 45° C.As shown in FIG. 53, all four cells comprising LHCEs showed much morestable cycling performance than cell using Si-baseline electrolyte,which showed a clear capacity decay. The capacity retentions for AE003,AE011, AE012 and AE013 after 400 cycles were 74.2%, 76.0%, 77.8% and80.0% respectively, while it was 21.9% for the Si-baseline electrolyteafter 200 cycles.

The corresponding CE during the cycling at 45° C. is shown in FIG. 54.All the cells with AE003, AE011, AE012 and AE013 showed higher averageCE above 99.8% during the cycling than 99.6% of Si-baseline, and thedetailed values are summarized in Table 12. Similar to 25° C., the CEfluctuation during the C rate change at every 50 cycles was smaller inthe LHCEs, indicating the resistance of the Si∥NMC622 was smaller in theLHCEs than the cell with Si-baseline electrolyte. Beyond that, fast CEfading showed after 100 cycles in the cell with baseline, while CE wasstable in the cells with LHCEs.

Other solvent-based LHCEs for Si/C-based LIBs: Investigated electrolytesare shown in Table 13.

TABLE 13 Electrolyte formulae Code Electrolyte formula E002ELiFSI:DME:TTE:EC = 1.0:1.1:3.0:0.2 by mol. E002F LiFSI:DME:TTE:FEC =1.0:1.1:3.0:0.2 by mol. E003F LiFSI:TMP_(a):TTE:FEC = 1.0:1.2:3.0:0.2 bymol. E009 LiFSI:TMS:TTE = 1.0:3.0:3.0 by mol. E009E LiFSI:TMS:TTE:EC =1.0:2.8:3.0:0.2 by mol. E009F LiFSI:TMS:TTE:FEC = 1.0:2.8:3.0:0.2 bymol.

Si/C and NCM811 electrodes were used to assemble Si/C∥NMC811CR2032-typecoin cells with 75 μL electrolyte. The cells were conducted threeformation cycles at C/20 for the first cycle and C/10 for the other twocycles before all the other electrochemical tests in the voltage rangeof 2.8-4.4 V, where 1C corresponds to a current density of 5.0 mA cm⁻².

FIG. 55A shows the voltage profiles of the first formation cycle at C/20for the Si/C∥NMC811 cells in different electrolytes. The cells withE002E, E002F, E003F, E009, E009E and E009F gave initial dischargecapacities of 3.50, 3.53, 3.41, 3.79, 3.56 and 3.36 mAh cm⁻²,respectively, which follows the order from high to low ofE009>E009E>E002F>E002E>E003F>E009F. When it turns to the cycling at C/3,this capacity order became different, indicating the different Lidiffusion abilities in these electrolytes. From FIG. 55B, after twoformation cycles, the reversible capacity of the cell with E002E was thehighest. And the order of the initial areal capacity from high to low atC/3 was E002E>E009E=E002F>>E009F>E003F>E009, with areal capacities of3.1, 3.0, 3.0, 2.3, 2.2 and 1.8 mAh cm⁻², respectively. After 200 cyclesat C/3, the reversible areal capacities of E002E, E009E, E002F, E009F,E003F and E009 were 2.5, 2.4, 2.5, 2.3, 1.8 and 2.1 mAh cm⁻²,respectively. Although the cell with E009F showed low areal capacity atthe initial cycles, it exhibited superior cycling stability with nocapacity loss after 200 cycles.

Other promising electrolyte additives for LHCEs are proposed to furtherimprove the cycling performance of Li-ion batteries with Gr, Si/C, andSi anodes and Ni-rich cathodes like NMC622, NMC811, and NMT. The IUPACnames and the abbreviations are summarized in Table 14.

TABLE 14 Electrolyte additives of interest for LHCEs Common name orIUPAC name abbreviation 1,3-dioxolan-2-one Ethylene carbonate (EC)1,3-dioxol-2-one Vinylene carbonate (VC) 4-Fluoro-1,3-dioxolan-2-oneFluoroethylene carbonate (FEC) 4-Methylene-1,3-dioxolan-2-one MEC4,5-Dimethylene-1,3-dioxolan-2-one DMEC 4-Vinyl-1,3-dioxolan-2-one VEC1,3,2-Dioxathiolan-2-oxide Prop-1-ene-1,3-sultone PES1-Methylsulfonylethene Methyl vinyl sulfone (MVS)1-Ethenylsulfonylethene Ethyl vinyl sulfone (EVS)1,3,2-Dioxathiolane-2,2-dioxide 1,3,2-Dioxathiane 2,2-dioxide DTDLithium 2-trifluoromethyl- LiTDI 4,5-dicyanoimidazole Lithiumbis(oxalato)borate LiBOB Lithium difluoro(oxalate)borate LiDFOB Lithiumhexafluorophosphate LiPF₆ 3-Methyl-1,4,2-dioxazol-5-one MDOTris(2,2,2-trifluoroethyl) TTFEPi phosphite 2-Oxo-1,3,2-dioxathiane1,3-Propylene sulfite (PS) Hexanedinitrile Adiponitrile ButanedinitrileSuccinonitrile Pentanedinitrile Glutaronitrile Tris(pentafluorophenyl)phosphine TPFP

Conducting salts and diluent solvents are also influential over theelectrochemical performance of the cells using LHCEs. Additionalexemplary conducting salts and diluents are listed in Table 15 and Table16, respectively.

TABLE 15 Other conducting salts Common name or IUPAC name abbreviationLithium LiTFSI bis(trifluoromethylsulfonyl)azanide Lithium LiBETIbis(pentafluoroethylsulfonyl)azanide Lithium(tetrafluoroethylenedisulfonyl)azanide Lithium LiFTFSI(fluorosulfonyl)(trifluoromethylsulfonyl)azanide Lithium LiTftrifluoromethanesulfonate

TABLE 16 Other diluent solvents Common name or IUPAC name abbreviation2-[bis(2,2,2- Tris(2,2,2- trifluoroethoxy)methoxy]-trifluoroethyl)orthoformate 1,1,1-trifluoroethane (TFEO)1,1,2,2,3,3,4,4-octafluoro-5- OTE (1,1,2,2-tetrafluoroethoxy)pentane1,1,1-Trifluoro-2-(2,2,2- Bis(fluoromethyl)ether trifluoroethoxy)ethane(BTFE)

Example 5 Further Evaluation of DME-Based Electrolytes for Cells withGraphite Anodes Experimental:

Electrolyte preparation, cell assembly and electrochemical performanceevaluations of Gr∥NMC811 cells: LiPF₆, EC, EMC, VC, FEC and DME, all inbattery grade, were purchased from Gotion, Inc. and used as received.LiFSI in battery grade was supplied by Nippon Shokubai Co., Ltd., andwas dried at 100° C. under vacuum overnight before use. TTE was orderedfrom SynQuest and dried with pre-activated molecular sieves till thewater content was less than 10 ppm by Karl Fisher titration. Theelectrolytes, whose formulae are summarized in Table 17, were preparedin an MBraun glovebox filled with purified argon where the contents ofboth oxygen and water were less than 1 ppm.

Laminates of Gr and NMC811 electrodes were obtained from the CellAnalysis, Modeling, and Prototyping (CAMP) Facility at Argonne NationalLaboratory (ANL), and their corresponding areal capacities were 1.84 mAhcm-2 and 1.45 mAh cm⁻², respectively. Disks of Gr (15.0 mm in diameter)and NMC811 (12.7 mm in diameter) were punched, dried at 110° C. undervacuum for at least 12 h, and then transferred into the argon-filledglovebox. CR2032 coin cell kits were ordered from MTI Corporation. Eachcoin cell was assembled with a piece of NMC811 disk, a piece ofpolyethylene separator (Asahi Hi-Pore, Japan), a piece of Gr disk, and50 μL electrolyte. To avoid the anodic corrosion of stainless steel athigh voltages, the aluminum (AI)-clad positive case was used and anadditional Al foil of 19.0 mm diameter placed in between the positivecathode disk and NMC811 cathode.

After cell assembly, the cells were placed in a temperature chamber(TestEquity TEC1) of 25° C., connected to a LAND Battery Testing System(CT2001A) and rested for 12 h. The formation cycles were consisted offirst charge/discharge cycle at C/20 rate and then two charge/dischargecycles at C/10 rate in the voltage range of 2.5-4.4 V, where 1C=1.45 mAcm⁻². For the long-term cycling performance evaluation, the testprocedure included three formation cycles and then consecutive 500cycles at C/3 charge and 1C discharge. For the C-rate capabilityevaluation, the cells were first conducted three formation cycles, andthen cycled by charging at C/5 and discharging at C/5, C/3, C/2, 1C, 2C,3C, 5C, and C/5. At each discharge C-rate, the charge/discharge cycleswere repeated for five times. All the electrochemical tests wereperformed at the temperature of 25.0±0.1° C.

Ionic conductivity evaluation: The ionic conductivities of the studiedelectrolytes were measured using a Bio-Logic MCS. During themeasurement, the temperature was increased to 60° C. and then decreasedto −40° C. in a stepwise manner (5° C./step). At each temperature step,the cell was held for 15 min and the ionic conductivities were measuredand recorded at the end of each step.

Ab initio molecular dynamics (A/MD) simulations of solvation structuresof the studied electrolytes: The AIMD simulations of the solvationstructures were performed in similar manner as described in our previouspublication (Jia et al., ACS Applied Materials & Interfaces 2020, 12(49), 54893-54903). The initial structure of eachsalt/solvent/additive/diluent mixture system was set up by randomlyplacing the numbers of LiFSI, DME, EC/FEC/VC, and TTE molecules on thebasis of the experimental densities and molar ratios. These initialgeometry structures were firstly minimized with molecular mechanicsmethod. These final structures were used as input structures for AIMDsimulations. The relaxed systems were pre-equilibrated for 5 ps in AIMDsimulations. The production time was 10 ps. A time step of 1 fs was usedin all AIMD simulations.

Diffusion ordered spectroscopy (DOSY) nuclear magnetic resonance (NMR)of the studied electrolytes: DOSY NMR experiments were performed on anAgilent DD2 500 spectrometer with a 5 mm HX z gradient One NMR probe.Larmor frequencies for these samples were 499.97, 470.39 and 194.32 MHzfor ¹H, ¹⁹F and ⁷Li, respectively. Gradient Compensated Stimulated Echowith Spin-Lock and Convection Compensation (DgcsteSL_cc) was used as theDOSY pulse sequence, which produced consistent results when testing aseries of diffusion delays on each sample. For this series ofexperiments a 60 ms diffusion delay in 16 steps were collected.Additionally, the diffusion gradient length was 2 ms for ¹H and ¹⁹Fspectra and the diffusion gradient length was 4 ms for ⁷Li spectra withthe maximum gradient strength from the Performa I gradient amp of 40G/cm. The Diffusion coefficient was calculated using the Stejskal-Tannerequation.

Post-mortem analyses on electrodes: The cycled cells were disassembledinside the argon-filled glovebox. The Gr anodes and the NMC811 cathodeswere retrieved from the cells, washed with fresh EMC (for E-Baseline) orDME (for LHCEs) to remove residual electrolytes, thoroughly dried undervacuum inside the antechamber of the glovebox, and subsequentlydelivered to do post-mortem characterizations in airtight vials.

XPS: XPS measurements were performed with a Physical ElectronicsQuantera Scanning X-ray Microprobe. This system uses a focusedmonochromatic Al Kα X-ray (1486.7 eV) source for excitation and aspherical section analyzer. The X-ray beam is incident normal to thesample, and the photoelectron detector is at 45° off-normal. High energyresolution spectra were collected using a pass-energy of 69.0 eV with astep size of 0.125 eV. The X-ray beam diameter was 100 μm and wasscanned over a 1200 μm×200 μm area of the sample.

TEM: Gr samples—The sample powder was scratched off the electrode diskand spread on a clean glass slide in the glovebox filled with argon.Subsequently, a lacey carbon TEM grid is placed on top of the powder(lacey carbon-side down). Thereafter, the TEM grid was loaded to a FEICompuStage High-Visibility, Low-Background, Double-Tilt Specimen Holder,which is subsequently loaded into the TEM. NMC811 samples—The NMC811samples were prepared according to the same procedure described in aprevious publication (Zhang et al., Advanced Energy Mater 2020, 10:2000368). A 300 kV FEI Titan monochromated (scanning) transmissionelectron microscope ((S)TEM) equipped with a probe aberration correctorwas used to acquire the bright-field image, selected area electrondiffraction (SAED), and high-resolution TEM image. All the samples wereimaged under low dose conditions (˜2 e Å⁻² s⁻¹ for low magnificationimaging, ˜200 e Å⁻² s⁻¹ for high resolution TEM imaging) to prevent beaminduced damage and artifacts.

Results and Discussion for the Improved Electrochemical Performance ofDME-Based LIBs:

Three DME-based LHCEs were prepared for the electrochemical performanceevaluation, in which the main components are LiFSI as solute, DME assolvating solvent and TTE as diluent, without or with small amounts ofadditives (EC and FEC). A conventional LiPF₆-organocarbonateselectrolyte was adopted as the baseline electrolyte (hereinafter,E-Baseline) for comparison. The detailed electrolyte formulae are listedTable 17.

TABLE 17 Formulations of the investigated electrolytes Name FormulationE-Baseline (E268) 1.0M LiPF₆ in (EC:EMC = 3.0:7.0 by wt.) + 2.0 wt. % VCE-DME (E002) LiFSI:DME:TTE = 1.0:1.1:3.0 by mol. E-DME-E (E002E)LiFSI:DME:TTE:EC = 1.0:1.1:3.0:0.2 by mol. E-DME-F (E002F)LiFSI:DME:TTE:FEC = 1.0:1.1:3.0:0.2 by mol.

Mechanistic insight to the extraordinary battery performances of E-DME-Eand E-DME-F: Due to the lone-pair electrons of oxygen atoms in itsstructure, DME exhibits a relatively high donor number (20.0), whichenables it to readily dissolve and dissociate Li salts. However, thenon-coordinated DME present in regular dilute electrolytes can beanodically decomposed at the surface of positive material at relativelylow voltages, making it unfavorable for high voltage operations. Inaddition to the anodic instability, DME in its dilute electrolytes isalso incompatible with the Gr anode, which probably originates from thelack of effective SEI formation ability. For these reasons, DME has beenconventionally considered as an inappropriate solvent candidate for theelectrolytes used in LIBs. However, after making LHCEs comprising DMEand adding a certain amount of additive (EC or FEC), excellent cyclingand rate performances of Gr∥NMC811 cells can be achieved even atrelatively high charge cut-off voltage of 4.4 V (FIGS. 41A-41B). Toelucidate the counterintuitive properties of E-DME-E and E-DME-F,comprehensive analyses and simulations, including AIMD simulations, DOSYNMR, XPS, TEM and XRD, were performed, where both E-Baseline and E-DMEwere employed as benchmark electrolytes.

A/MD simulations: It is well acknowledged that the SEI on Gr electrode,being predominant over the electrochemical performances of LIBs, isformed by the decomposition products of electrolyte in the initialcycles. The compositions and properties of the SEI are stronglydependent on the salt anion, solvent, additive, and solvation structure,i.e., the composition and structure of cation solvation sheath of theelectrolyte. Therefore, prior to SEI studies, it is indispensable toelucidate the microscopic structure of the electrolyte. The solvationstructures of the 1.0-1.2 M LiPF₆-organocarbonates electrolytes werewell studied. It is generally accepted that the cation solvationsheathes in these electrolytes are primarily comprised of Li⁺coordinated by 2-5 cyclic carbonate molecules, such as EC and/or othercyclic carbonate additives in the inner solvation sheath. The solvationstructures of the DME-based LHCEs are expected to be different fromthose of the conventional electrolytes. To elucidate the solvationstructures of the DME-based LSEs, AIMD simulations were performed forE-DME, E-DME-E and E-DME-F. AIMD showed that DME and LiFSI tend to formclusters in TTE in E-DME, being consistent with the conclusion drawn inprevious publications (Chen et al., Advanced Materials 2018,30(21):1706102). TTE has very weak (if any) affinity to Li⁺ due to thestrong electron withdrawing effect of fluorine (F) atoms in itsmolecule. After the addition of small portion of additive, EC or FEC,into E-DME, the cluster structures in E-DME are not damaged. Comparedwith DME, these additives (EC/FEC) show an even stronger affinity toLi⁺, as the length of Li⁺→EC/FEC coordination bond is slightly shorterthan that of Li⁺→DME bond, as indicated by the radial distributionfunction (see FIGS. 56A-56C). The radial distribution function betweenLi⁺ and the O atoms of DME, FSI⁻, TTE, EC and FEC in the E-DME, E-DME-Eand E-DME-F electrolytes was obtained from the AIMD simulations. Asshown in FIG. 56A, the strong peaks of Li—O(DME) and Li—O(FSI) wereobserved in E-DME, suggesting that Li⁺ has a strong affinity with bothDME and FSI⁻ in the ion-sheath cluster. In comparison, Li—O(TTE) did notshow any apparent peaks. After the addition of EC (FIG. 56B) or FEC(FIG. 56C) into the E-DME, the strong Li—O(EC or FEC) peaks wereobserved. Compared with the Li—O(DME), the peak position of Li—O(EC orFEC) peaks was closer to the y-axis, indicating a shorter bond length.In other words, the introduced additives had an even stronger affinityto the Li⁺ than the DME molecules. According to the simulation results,it can be inferred that the formation of FSI⁻—Li⁺-DME(-EC/FEC) clustersare energetically favorable.

Diffusion coefficient determination: To obtain a deeper understanding onthe solvation structures, ¹H, ¹⁹F and ⁷Li DOSY NMR measurements wereperformed for the four studied electrolytes. The self-diffusioncoefficients are summarized in FIGS. 57A-57B.

As shown in FIG. 57A, in E-Baseline, the self-diffusion coefficient ofthe cation is lower than that of the anion, which can be assigned to itslarger, more sluggish cation solvation sheath. In the LHCEs (FIG. 57B),the self-diffusion coefficients of Li⁺, FSI—, DME were relativelysimilar, implying that the ion sheath clusters are relatively stable,and they mainly migrate as a whole in the LHCEs. However, theinterchange between ion clusters also takes place as the diffusioncoefficients are not identical. The self-diffusion coefficient of TTE issignificantly larger than those of ion sheath cluster constituents,reaffirming that TTE has a relatively low affinity to the ion-sheathclusters and acts as a diluent in the DME-based HCEs. It should be notedthat the diffusion coefficients of the additives cannot be accuratelyquantified, due to their low peak intensities in the spectra. Onaverage, the self-diffusion coefficients of the species in the threeDME-based LHCEs were lower than those of E-Baseline, which can beassigned to the higher viscosities of these DME-based LHCEs (FIG. 39A).Based on the self-diffusion coefficients, the transference numbers ofE-baseline, E-DME, E-DME-E and E-DME-F were determined as 0.41, 0.55,0.56 and 0.57, respectively.

Li salt dissociation degree determination: Based on the diffusioncoefficients obtained from the DOSY NMR and the ionic conductivities(FIG. 39B), the dissociation degrees of conducting salts in the selectedelectrolytes can be determined by the modified Nernst-Einstein equation:

$\sigma = {\alpha\;\frac{{Ne}^{2}}{k_{B}T}\left( {D_{+} + D_{-}} \right)}$

where, σ is the measured ionic conductivity; a, the dissociation degree;N, the number density of the lithium salt; e, the elementary charge, kB,the Boltzmann constant; T, the temperature; and D₊ and D⁻, theself-diffusion coefficients of cation and anion; respectively (Hayamizu,Journal of Chemical and Engineering Data 2012, 57(7):2012-2017).

In the case of the conventional electrolyte, E-Baseline, thedissociation degree was quantified to be 68.8%. In comparison, thedissociation degrees of E-DME, E-DME-E and E-DME-F were determined as15.5%, 17.7% and 17.9%, respectively, being significantly lower thanthat of E-Baseline. The dissociation degrees of the studied electrolytescorrespond well to the results obtained by AIMD simulations. Since TTEmolecules barely participate in the solvation with Li⁺, the scarcity ofsolvating molecules (DME) creates a significant proportion (>80%) ofnon-dissociated ion pairs in DME-based LHCEs. The addition of a smallamount of EC or FEC into E-DME can slightly increase the dissociationdegree of the LHCEs, due to the increased number of solvating molecules.

Combining the results obtained from AIMD and DOSY NMR, it can beconcluded that the solvation structures of DME-based LHCEs aredistinctive from that of E-Baseline. In E-Baseline, the solvation sheathis mainly comprised of Li⁺-(ECNC)_(n). In contrast, the solvation sheathis comprised of several FSI⁻—Li⁺-(DME/additive)_(n) clusters inDME-based LHCEs, and most of the Li⁺—FSI⁻ exists as non-dissociated ionpair. The addition of a small amount of EC and FEC into DME based LSEchanges the composition of the solvation sheath while keeping the uniquesolvation structure intact.

Influence of the solvation structure on the SEI composition: The SEIformation on Gr is comprised of three consecutive procedures: (1)co-intercalation of the solvation sheath into the graphene layer, (2)expansion of Gr lattice, and (3) decomposition of the solvation sheath.For this reason, the composition and structure of the ion sheath play ahighly influential role in the SEI formation on Gr. To study theinfluence of the unique solvation structure of LHCEs on the SEIformation, the compositions of the SEIs formed in these fourelectrolytes were systematically analyzed by XPS after three formationcycles and 500 cycles.

The atomic concentrations of different elements in SEIs after theformation cycles are summarized in FIG. 58. In E-Baseline, thecharacteristic element of the conducting salt (LiPF₆) is phosphorus (P).As determined by XPS, the atomic concentration of P in SEI formed inE-Baseline was lower than 0.5%. It suggests that the anions play arelatively weak role in the formation of SEI in the conventional 1 molL⁻¹ LiPF₆-organocarbonates electrolyte, because the dissociated anionsare electrostatically repelled by the negative charge of the Grelectrode during the first charge cycle. In comparison, significantamounts of N and S were detected in the SEs formed in all threeDME-based LHCEs. Since more than 80% of Li salt exists asnon-dissociated ion pairs in the DME-based LHCEs, the non-dissociatedanions also participate in the SEI formation process, which isrepresented as a significant amount of N and S in the SEIs formed in theDME-based LHCEs. With this, it can be concluded that the uniquesolvation structure of DME-based LHCEs promotes the participation ofanions in the SEI formation process.

The detailed XPS spectra of selected elements in the SEs formed in thestudied electrolytes after formation cycles are shown in FIG. 59. Asillustrated in C 1s and O 1s spectra in FIG. 59, the concentration ofLi₂CO₃ (290.3 eV in C1s spectra and 532.0 eV in O 1s spectra) wassignificantly higher in E-Baseline SEI than those of LHCE SEIs. Inaddition, the carbonate esters (R—CO₃—R′, 533.8 eV in O1s spectra) weredetected in the SEI formed in E-baseline, which cannot be detected inSEIs formed in LHCEs. These species mainly originate from thedecomposition of Li⁺-(EC/VC)_(n) solvation sheath. In the F 1s spectra,two species were identified in all the SEs: (1) the organic C—F species(at 688.0 eV) and (2) the inorganic LiF species (684.8 eV). The C—Fspecies mainly originate from the PVDF binder and the LiF mainlyoriginates from the Li salt decomposition. Compared with the E-BaselineSEI, the percentages of LiF in LHCE SEs were significantly higher, whichsuggests that the anions in DME-based LHCEs play a more active role thanin E-Baseline. In the N 1s and S 2p spectra, the decomposition productsof the anions were identified as amines, Li₃N, sulfates, Li dithionate,and Li_(x)S_(y), many of which are highly ionically conductive. Asillustrated in FIG. 42, E-DME-E (E002E) cells and E-DME-F (E002F) cellsexhibited comparable or even better C-rate performance than theE-Baseline (E268) cells, despite the conductivities of E-DME-E andE-DME-F are significantly lower than that of E-Baseline. The highlyionically conductive species in SEs identified by XPS are considered tocontribute to the excellent C-rate performance of E-DME-E and E-DME-Fcells.

After 500 cycles at C/3 charge and 1C discharge, significant compositionchange was observed in the SEIs formed in E-Baseline and E-DME (FIG.60). In the SEI formed in E-baseline, the contents of ether species(—C—O—C—, 286.5 eV in C 1s), Li₂CO₃ (290.3 eV in C1s spectra and 532.0eV in O 1s spectra) and carbonate esters (R—CO₃—R′, 533.8 eV in O1sspectra) exhibited substantial increase after long-term cycling, whichcould be assigned to the accumulated decomposition of the electrolyte.New species such as LiPO_(x)F_(y) were also detected, which can beassigned to the decomposition of chemically unstable LiPF₆ salt.Significant contents increase of ether species (—C—O—C—, 286.5 eV in C1s), Li₂CO₃ (290.3 eV in C1s spectra and 532.0 eV in O 1s spectra) werealso observed in the SEI formed in E-DME. After formation cycles, Li₂Owas observed in the SEs formed in E-baseline and E-DME (FIG. 59),however it is not visible after long-term cycling performanceevaluation. A probable explanation is that the Li₂O signal is obscuredby the propagated SEI.

As for the SEIs formed in E-DME-E and E-DME-F electrolytes after 500cycles, only minor changes, i.e. slight increases in ether species andthe species transformation from Li₃N to Li_(x)NO_(y), were observed,while the proportion of other species remained almost the same.

Based on the XPS spectra, it can be concluded that the unique solvationstructure of LHCEs facilitates the participation of the anions in theSEI formation process, whereas the SEI in E-Baseline is predominantlycomprised of the decomposition products of the solvating solvent. Theanion derived decomposition products in LSE SEI possibly contribute to ahigher ionic conductivity of the SEI. Meanwhile, the SEIs formed inE-DME-E and E-DME-F are more stable in composition compared with thoseformed in E-Baseline and E-DME with prolonged cycling.

Morphology evolution of SEI over long-term cycling: After the formationcycles, the morphologies of SEIs formed on Gr electrodes in the studiedelectrolytes were characterized by TEM. The results are summarized anddepicted in FIGS. 61A-D. As illustrated in FIG. 61A, after the formationcycles in E-Baseline, the Gr particle was encapsulated by an SEI layerwith the thickness range of 1.5-3.0 nm. In comparison, the Gr particlewas covered by a thick and non-uniform SEI of 10.3 nm in E-DME (FIG.61B). It reaffirms that, although E-DME (E002) (i.e. DME-based LSEwithout additive) can facilitate the formation of SEI that enablesreversible charge/discharge cycling of the Gr∥NMC811 cells (FIGS. 40A,41A), the SEI formation process was achieved at the cost of significantamount of electrolyte decomposition and active Li loss. In addition,certain degrees of Gr exfoliation were observed (marked by yellow dashlines in FIG. 61B). Both the thick SEI and the partial Gr exfoliationindicated that the SEI formed in E-DME was not sufficiently effective.For this reason, the specific capacity of E-DME based cells merelyamounted to 142.8 mAh g⁻¹ after three formation cycles, as illustratedin FIG. 40A. However, after the introduction of an additive, EC or FECinto E-DME, the morphology of the SEI was effectively improved. In thecase of E-DME-E, an ultrathin (about 1.2 nm, FIG. 61C) and uniform SEIwas formed on Gr particles after three formation cycles. In the case ofE-DME-F, the SEI thickness was slightly thicker (4.0 nm, FIG. 61D).Unlike in the additive-free electrolyte E-DME, Gr particles did notexhibit partial exfoliation in E-DME-E and E-DME-F after formationcycles. Consequently, the irretrievable capacity losses of E-DME-E andE-DME-F cells in the first formation cycle was substantially reduced(FIGS. 40A and 40B). Evidently, the morphology of the SEI issignificantly influenced by the electrolyte additive.

It is well accepted that the SEI evolution in LIBs is the major“culprit” accountable for the capacity decay of LIBs. For this reason,follow-up studies on SEI evolution over long-term cycling areindispensable to the understanding how the selected electrolytesinfluence the cycle life of Gr∥NMC811 cells. After 500 charge/dischargecycles, post-mortem TEM measurements were performed for the Gr particlesretrieved from the Gr∥NMC811 cells. As revealed in FIG. 61E, thethickness of SEI increased significantly by 10 nm in E-Baseline, whichis possibly the major contributor to the relatively rapid capacity decayof E-Baseline cells. In the case of E-DME, the thickness growth was notas severe as that in E-baseline. However, as illustrated in FIG. 61F,the partial exfoliation of Gr particles (marked by yellow dash lines)aggravated over long-term cycling. Similarly, partial exfoliation wasalso observed in E-DME-E cells (FIG. 61G). The gradually aggravatedpartial exfoliation is assumed to be the reason behind the gradualcapacity increase of E-DME (E002) and E-DME-E (E002E) cells upon cyclingfor certain cycles, as shown in FIG. 41A. To study the degree of the Grexfoliation after long term cycling, XRD were performed for the of thegraphite particles retrieved from the cells. The XRD patterns of thepowders were obtained by loading them into thin-walled glass capillaries(0.5 mm diameter, Charles Supper Co., MA). These were mounted into aRigaku D-Max Rapid II micro-diffractometer equipped with a rotating Cranode (λ=2.2910 Å). The X-rays generated passed through a collimator 300μm in diameter onto a portion of the sample and the diffracted signalrecorded on a 2D image plate during a 10-minute exposure. The 2D signalwas subsequently integrated between 10 and 150° 2θ to give conventional1D diffraction traces. As shown in FIGS. 62A-62B, no apparent differencein XRD patterns was observed for the Gr particles after 500charge/discharge cycles in the four studied electrolytes, despitepartial exfoliation confirmed by TEM in E-DME and E-DME-E samples. Itshould be noted that TEM takes a relatively local perspective whereasXRD takes a global perspective. If the partial exfoliation only occursin some parts on Gr particle, the change in the crystal structure may belower than the detection limit of XRD. This confirmed that exfoliationonly occurs in a small proportion of Gr particles and the change in thecrystal structure is lower than the detection limit of XRD. In contrast,the SEI formed in E-DME-F was highly effective against solventco-intercalation and partial Gr exfoliation, and the thickness of thisSEI only increased by 2 nm after 500 cycles (FIG. 61H). For this reason,E-DME-F cells exhibited excellent capacity retention after the long-termcycling performance.

With this, it can be concluded that the composition of the solvationsheath (tuned by additives), plays a highly influential role in SEIformation process as well as the evolutions of SEIs in LHCEs. The SEIformed in E-DME-F is the most effective one as it protects the Grparticles not only from exfoliation but also the parasitic reactions atthe interface between electrolyte and SEI.

Influence of electrolyte on cathode material: The compatibility of theDME-based electrolytes with the cathode materials should also beconsidered. According to the previous publications, the E-DME exhibitsexcellent anodic stability with NMC electrode in Li metal batteries (Renet al., Joule 2019, 3(7):1662-1676). To verify this, the anodicstability windows of the studied electrolytes were evaluated inLi∥LiMn₂O₄ according to literature (Kasnatscheew et al., PhysicalChemistry Chemical Physics 2017, 19(24):16078-16086). The anodicstabilities of the E-Baseline, E-DME, E-DME-E and E-DME-F weredetermined as 4.7, 4.6, 4.6 and 4.6 V, respectively (FIG. 63),suggesting that the studied electrolytes are expected to be anodicallystable against NMC811 at the cut-off voltage of 4.4 V. It was confirmedby the XPS spectra of NMC materials that the decompositions of theselected electrolytes on NMC811 were not severe, even after 500charge/discharge cycles.

To obtain a deeper understanding of the interaction between the NMC811cathode and the selected electrolytes, TEM images were taken for theNMC811 electrodes after formation cycles and long-term cyclingperformance evaluations. The results are summarized in FIGS. 64A-64H.After the formation cycles, a rock-salt layer of transition metal oxidecan be observed in all the NMC811 samples (FIGS. 64A-64D). The phasetransition of NMC811 from a layered structure to a rock-salt structureis considered to originate from the intrinsic structural instability ofthe cathode material at relatively high delithiation state. Such processcan be catalyzed by the acidic impurities in the electrolyte. After 500charge/discharge cycles, the thickness of rock-salt layer of NMC811 inE-baseline propagated to more than 20 nm (see FIGS. 64A, 64E). A mixedlayer of small crystalline domains and amorphous species was alsoobserved on top of the rock-salt layer (FIG. 64E). It is widely acceptedthat the LiPF₆ can readily lead to the generation of acidic species ofHF in electrolytes, which accounts for the severe NMC811 degradation(Jia et al., Chemistry of Materials 2019, 31(11):4025-4033).

In comparison, E-DME and E-DME-E samples exhibited negligible structurechanges after 500 charge/discharge cycles (FIGS. 64B, 64F, and FIGS.64C, 64G, respectively). The difference could be probably assigned tothe better chemical stability of LiFSI than LiPF₆. However, NMC811cycled in E-DME-F also exhibited significant phase transition, as asignificant proportion of the material changed from layer structure torock-salt structure (FIG. 64H). The reason could be assigned to thepresence of FEC in the electrolyte. It was considered that FEC couldalso lead to the formation of HF in the electrolyte, which in turnfacilitates the phase transition of NMC811. Despite that the phasetransition from layered structure to rock-salt structure leads to theincreased impedance of the cell, E-DME-F still achieved an excellentcycling performance in Gr∥NMC811 cells, which could be probably assignedto the fact that the beneficial effects of FEC on the Gr SEI overweighsits negative impact on the cathode material.

Conclusions: In this work, the concept of LHCE was adopted to developDME-based electrolytes for Gr∥NMC811 cells operated at a charge cut-offvoltage of 4.4 V. Compared with cells using a typicalLiPF₆-oragnocarbonates electrolyte (E-Baseline), cells using E-DME-E(with EC as additive) and E-DME-F (with FEC as additive) exhibitedsuperior long-term cycling performance and comparable C-rateperformance. As revealed by the mechanistic studies, the DME-based LHCEsexhibited distinctive solvation structures, in which several LiFSI saltmolecules and DME/additive molecules form a cluster as the solvationsheath and most of the LiFSI molecules in the cluster exist asnon-dissociated ion pairs. Such salt-solvent/additive clusters promotethe participation of salt anions in the SEI formation process. Theresulting SEIs can enable long-term charge/discharge cycles. Inaddition, the lack of free DME molecules in DME-based LHCEs extends theanodic stability of these electrolytes.

A highly beneficial synergetic effect was observed between theelectrolyte additive and the unique solvation structure of DME-basedLHCEs. The addition of a small amount of electrolyte additives, such asEC and FEC, does not change the unique solvation structure of LHCEs.However, the additives effectively suppress active Li loss in theformation cycles, improve the C-rate performance and extend the cyclelife of Gr∥NMC cells. Among all the studied electrolytes, E-DME-F isconsidered to be the most promising electrolyte, because a highlyeffective SEI is formed by the synergy between FEC and the solvationstructure. The SEI exhibited extremely low growth rate over long-termcycling performance evaluation as well as effectively suppressed partialexfoliation of Gr particles. Consequently, the Gr∥NMC811 cells achievedan excellent capacity retention of 86.8% after 500 charge/dischargecycles. Based on these findings, it was demonstrated that, by tuning thestructure and composition of the solvation sheath, an ether solvent thatwas conventionally considered to be incompatible with Gr electrode andunstable above 4 V can be engineered as an appropriate solvent forelectrolytes that enable long cycle life and high rate capability ofGr-based, high-voltage LIBs (Gr∥NMC811 cells charged to 4.4V).

In view of the many possible embodiments to which the principles of thedisclosed invention may be applied, it should be recognized that theillustrated embodiments are only preferred examples of the invention andshould not be taken as limiting the scope of the invention. Rather, thescope of the invention is defined by the following claims. We thereforeclaim as our invention all that comes within the scope and spirit ofthese claims.

We claim:
 1. An electrolyte, comprising: a lithium salt; a nonaqueoussolvent comprising at least one of the following components: (i) anester, (ii) a sulfur-containing solvent, (iii) a phosphorus-containingsolvent, (iv) an ether, (v) a nitrile, or any combination thereof,wherein the lithium salt is soluble in the solvent; a diluent comprisinga fluoroalkyl ether, a fluorinated orthoformate, a fluorinatedcarbonate, a fluorinated borate, or a combination thereof, wherein thelithium salt has a solubility in the diluent at least 10 times less thana solubility of the lithium salt in the solvent; and an additive havinga different composition than the lithium salt, a different compositionthan the solvent, and a different composition than the diluent, theelectrolyte having a lithium salt-solvent-additive-diluent molar ratioof 1:x:y:z where 0.5≤x≤5, 0≤y≤1, and 0.5≤z≤5.
 2. The electrolyte ofclaim 1, wherein the lithium salt comprises lithiumbis(fluorosulfonyl)imide (LiFSI), lithiumbis(trifluoromethanesulfonyl)imide (LiTFSI), lithium(fluorosulfonyl)(trifluoromethylsulfonyl)imide (LiFTFSI), lithiumbis(pentafluoroethanesulfonyl)imide (LiBETI), lithiumtrifluoromethanesulfonate (LiTf), lithium bis(oxalato)borate (LiBOB),LiPF₆, LiAsF₆, LiBF₄, LiCF₃SO₃, LiClO₄, lithium difluoro(oxalato)borate(LiDFOB), LiI, LiBr, LiCl, LiSCN, LiNO₃, LiNO₂, Li₂SO₄, or anycombination thereof.
 3. The electrolyte of claim 1, wherein thenonaqueous solvent comprises dimethyl carbonate (DMC), ethyl methylcarbonate (EMC), diethyl carbonate (DEC), ethylene carbonate (EC),propylene carbonate (PC), difluoroethylene carbonate (DFEC),trifluoroethylene carbonate (TFEC), trifluoropropylene carbonate (TFPC),methyl 2,2,2-trifluoroethyl carbonate (MFEC), ethyl acetate, ethylpropionate, methyl butyrate, ethyl trifluoroacetate,2,2,2-trifluoroethyl acetate, 2,2,2-trifluoroethyl trifluoroacetate,dimethyl sulfone (DMS), ethyl methyl sulfone (EMS), ethyl vinyl sulfone(EVS), tetramethylene sulfone (TMS), dimethyl sulfoxide, ethyl methylsulfoxide, trimethyl phosphate (TMP_(a)), triethyl phosphate (TEP_(a)),tributyl phosphate, triphenyl phosphate, tris(2,2,2-trifluoroethyl)phosphate, bis(2,2,2-trifluoroethyl) methyl phosphate, trimethylphosphite, triphenyl phosphite, tris(2,2,2-trifluoroethyl) phosphite,dimethyl methylphosphonate, diethyl ethylphosphonate, diethylphenylphosphonate, bis(2,2,2-trifluoroethyl) methylphosphonate,hexamethylphosphoramide, hexamethoxyphosphazene(cyclo-tris(dimethoxyphosphonitrile), hexamethoxycyclotriphosphazene),hexafluorophosphazene (hexafluorocyclotriphosphazene),1,2-dimethoxyethane (DME), diethylene glycol dimethyl ether (diglyme),triethylene glycol dimethyl ether (triglyme), tetraethylene glycoldimethyl ether (tetraglyme), 1,3-dioxolane (DOL), allyl ether,acetonitrile, propionitrile, or any combination thereof.
 4. Theelectrolyte of claim 1, wherein the additive comprises EC,fluoroethylene carbonate (FEC), vinylene carbonate (VC),4-vinyl-1,3-dioxolan-2-one (vinyl ethylene carbonate, VEC),4-methylene-1,3-dioxolan-2-one (4-methylene ethylene carbonate, MEC),4,5-dimethylene-1,3-dioxolan-2-one, prop-1-ene-1,3-sultone (PES),1,3,2-dioxathiolane-2-oxide, 1,3,2-dioxathiolane-2,2-dioxide,1,3,2-dioxathiane-2,2-dioxide (DTD), lithium2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI), LiDFOB), lithiumhexafluorophosphate, 3-methyl-,4,2-dixoazol-5-one (MDO),tris(2,2,2-trifluoroethyl) phosphite (TTFEPi), 2-oxo-1,3,2-dioxathiane,butanedinitrile, pentanedinitrile, hexanedinitrile,tris(pentafluorophenyl) phosphine, 1-methylsulfonylethene,1-ethenylsulfonylethane, or any combination thereof.
 5. The electrolyteof claim 1, wherein: (i) the additive comprises EC, FEC, VC, or acombination thereof; or (ii) y is 0.1-0.5; or (iii) both (i) and (ii).6. The electrolyte of claim 1, wherein: the nonaqueous solvent comprisesa carbonate other than EC, FEC, or VC; and the additive comprises 2 wt %to 10 wt % FEC and 0.1 wt % to 2 wt % VC.
 7. The electrolyte of claim 1,wherein the diluent comprises1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE),bis(2,2,2-trifluoroethyl) ether (BTFE), 1H,1H,5H-octafluoropentyl1,1,2,2-tetrafluoroethyl ether (OTE), 1,2,2,2-tetrafluoroethyltrifluoromethyl ether, heptafluoroisopropyl methyl ether,tris(2,2,2-trifluoroethyl) orthoformate (TFEO), bis(2,2,2-trifluoroethylcarbonate), tris(2,2,2-trifluoroethyl) borate, or any combinationthereof.
 8. The electrolyte of claim 1, wherein the nonaqueous solventcomprises DMC, DME, TMS, TMP_(a), TEP_(a), or any combination thereof.9. The electrolyte of claim 8, wherein: (i) the salt comprises LiFSI; or(ii) the diluent comprises TTE, BTFE, OTE, or any combination thereof;or (iii) the additive comprises EC, FEC, VC, or any combination thereof;or (iv) any combination of (i), (ii), and (iii).
 10. The electrolyte ofclaim 1, wherein 0.5≤x+y≤4.5.
 11. The electrolyte of claim 1, wherein:x=0.5-3.5; y=0.01-0.8; and z=1-4.
 12. The electrolyte of claim 1,wherein: (i) y=0.15-0.25; or (ii) x+y=2-3; or (iii) both (i) and (ii).13. The electrolyte of claim 1, wherein: x=1.6-2.8; y=0.2-0.6;x+y=2.2-3.0; and z=3.
 14. The electrolyte of claim 1, wherein theelectrolyte consists essentially of the lithium salt, the solvent, thediluent, and the additive.
 15. A battery system, comprising: anelectrolyte according to claim 1; an anode, where the anode is acarbon-based anode, a silicon-based anode, or a silicon/carboncomposite-based anode; and a cathode.
 16. The battery system of claim15, wherein the cathode comprises Li_(1+w)Ni_(x)Mn_(y)Co_(z)O₂(x+y+z+w=1, 0≤w≤0.25), LiNi_(x)Mn_(y)Co_(z)O₂ (x+y+z=1), LiCo₂,LiNi_(0.8)Co_(0.15)Al_(0.05) O₂, LiNi_(0.5)Mn_(1.5)O₄ spinel, LiMn₂O₄,LiFePO₄, Li_(4−x)M_(x)Ti₅O₁₂ (M=Mg, Al, Ba, Sr, or Ta; 0≤x≤1), MnO₂,V₂O₅, V₆O₁₃, LiV₃O₈, LiM^(C1) _(x)M^(C2) _(1−x)PO₄ (M^(C1) or M^(C2)=Fe,Mn, Ni, Co, Cr, or Ti; 0≤x≤1), Li₃V_(2−x)M¹ _(x)(PO₄)₃ (M¹=Cr, Co, Fe,Mg, Y, Ti, Nb, or Ce; 0≤x≤1), LiVPO₄F, LiM^(C1) _(x)M^(C2) _(1−x)O₂((M^(C1) and M^(C2) independently are Fe, Mn, Ni, Co, Cr, Ti, Mg, or Al;0≤x≤1), LiM^(C1) _(x)M^(C2) _(y)M^(C3) _(1−x−y)O₂ ((M^(C1), M^(C2), andM^(C3) independently are Fe, Mn, Ni, Co, Cr, Ti, Mg, or Al; 0≤x≤1;0≤y≤1), LiMn_(2−y)X_(y)O₄ (X=Cr, Al, or Fe, 0≤y≤1),LiNi_(0.5−y)X_(y)Mn_(1.5)O₄ (X=Fe, Cr, Zn, Al, Mg, Ga, V, or Cu;0≤y<0.5), xLi₂MnO₃.(1−x)LiM^(C1) _(y)M^(C2)M^(C3) _(1−y−z)O₂ (M^(C1),M^(C2), and M^(C3) independently are Mn, Ni, Co, Cr, Fe, or mixturethereof; x=0.3-0.5; y≤0.5; z≤0.5), Li₂M²SiO₄ (M²=Mn, Fe, or Co),Li₂M²SO₄ (M²=Mn, Fe, or Co), LiM²SO₄F (M²=Fe, Mn, or Co),Li_(2−x)(Fe_(1-y)Mn_(y))P₂O₇ (0≤y≤1), Cr₃O₈, Cr₂O₅, a carbon/sulfurcomposite, or an air electrode.
 17. The battery system of claim 15,wherein: the cathode comprises LiNi_(x)Mn_(y)Co_(z)O₂ where x≤0.6 orLiNi_(x)Mg_(y)Ti_(1−x−y)O₂ where 0.9≤x<1; and the anode is agraphite-based anode, a silicon-based anode, a silicon/graphitecomposite-based anode comprising 10 wt % to 90 wt % graphite and 5 wt %to 90 wt % silicon, or a silicon/graphite composite anode comprisingcarbon-coated silicon with a carbon content of 5 wt % to 55 wt %. 18.The battery system of claim 15, wherein the battery system exhibits: (i)a first cycle Coulombic efficiency of at least 75%; or (ii) an averageCoulombic efficiency of at least 98% over 500 cycles at 25° C. afterthree formation cycles; or (iii) an average Coulombic efficiency of atleast 99.7% after 200 cycles; or (iv) a capacity retention of at least85% after 500 cycles at 25° C. compared to the first cycle after threeformation cycles; or (v) a capacity retention of at least 90% from350^(th) cycle to 500^(th) cycle; or (vi) any combination of (i), (ii),(iii), (iv), and (v).
 19. The battery system of claim 15, wherein: thelithium salt comprises LiFSI; the solvent comprises DME, DMC, TMP_(a),or TMS; the diluent comprises TTE or OTE; and the additive comprises VC,EC, FEC, or any combination thereof.
 20. The battery system of claim 15,wherein: (i) the battery system is operable at a voltage 2.5 V to 4.5 V;or (ii) the battery system is operable over a temperature range of from−30° C. to 60° C.; or (iii) both (i) and (ii).